E21. (a) (i) The majority of candidates correctly substituted the data into the equation and calculated a correct answer.
(ii) This was generally answered well. Unfortunately, a number of candidates chose to draw several arrows rather than the requested single arrow.
(b) This part of the question was answered well but there were some instances where candidates had given the momentum as 900 then explained the reason by substituting numerical values for the mass and velocity and presented the equation ‘900 × 0 = 900’.
E23. (a) (i) There was much confusion throughout this question between momentum and energy. Clearly a large number of candidates consider them to be the same. Less than half of the candidates gave a correct answer. Those that did often scored the mark with a simple statement such as ‘momentum before = momentum after’.
(ii) Very few candidates answered this correctly. Incorrect answers often talked about elastic and inelastic collisions in terms of energy conservation. There were also a lot of references to crumple zones, walls, immovable objects etc. Those candidates gaining credit often simply stated an ‘external force acts’.
(b) (i) Many candidates scored 1 mark for calculating the momentum of the car either before or after. However, many candidates failed to develop the idea and subtract the two numbers. Units proved troublesome; far too often it was given as kg/m/s or kgm/s2, occasionally answers were given as N.
(ii) The better, well prepared candidates scored both marks. However, the incorrect answer 10 - 2 = 8 m/s was very common. Too few candidates seemed able to write down ‘momentum before =; momentum after’ and hence obtain the answer.
E24. (a) This question was answered well with a majority of the candidates achieving both marks. However, there were some responses which indicated that candidates had interpreted ‘m/s’ as being momentum per second. Some candidates thought that R had the most momentum because it was in front.
(b) (i) Most candidates were able to multiply the mass by the velocity correctly. However, a significant minority of candidates substituted the numbers correctly but seemed not to have a calculator to enable them to give the correct answer.
(ii) The majority of candidates responded correctly with errors being equally split between the two wrong answers provided. A few candidates had unfortunately tried to split the correctly paired unit circling only either kg or m/s.
(c) (i) This question was answered well with most candidates responding in terms of an increase in reaction time although some incorrect responses were clearly directed towards distance, rather than time.
(ii) This question was poorly answered mainly due to candidates not answering the question set ie, what happens to braking distances in wet conditions.
Candidates wrote excellent responses in terms of aquaplaning, skidding, lack of traction, wet brakes, the need to brake earlier, the need for less braking force, the increased possibility of accidents, the need to drive slower, etc. However, these responses failed to address the question.
E25. (a) Many candidates obtained the correct answer having correctly calculated the resultant force as 1155 N. Correct calculation of the force 1155 N then multiplying by the mass of 275 kg was a common error gaining just one mark. The use of an incorrect force with the correct method, gained many candidates one compensatory mark.
(b) (i) Many candidates failed to understand that the question was referring to the validity of the data with many answers given in the form of a conclusion rather than answering the question about valid data. Those candidates who realised the question was about the data, answered mainly in terms of the reliability of police files (YES) or on the lack of information about ages (NO). Many candidates quoted the number of files in the source, but as they failed to express whether this was a large or a small sample, failed to score a mark for this. There was also evidence of much rewriting of answers, mostly to little or no advantage.
(ii) Just over half of candidates gained one mark for describing how the smaller motorbikes had more accidents and a small minority of candidates went on to note how there were fewer smaller bikes than larger bikes, or calculated ratios.
(c) (i) Very few candidates gained full marks on this question, in spite of it being a well examined aspect of the course. A change in context does disguise what is needed to all but the highest scoring candidates, in spite of the stem referring to momentum. Over half of candidates scored zero. The quality of the explanation was often poor. There are still a large number of answers referring to cushioning the impact rather than reducing the force. The‘decreases rate of change of momentum’ is the most frequently missed mark. A number of candidates confused their response with references to kinetic energy and stopping distances.
(ii) Most candidates gave the answer that the new safety barriers would save lives, or reduce injuries, which gained the mark. Those who thought that 17m/s was too slow to crash or cause serious injury had confused the unit with mph.‘Money could be better spent’ was rarely a complete answer and so did not score a mark very often.
E26. (a) This question was generally answered well with virtually all candidates recognising that drinking alcohol would increase the chance of an accident occurring. However, a number of candidates failed to achieve the second mark due to identifying that there would be an alteration of the driver’s reactions, but not whether the alteration would be positive or negative. Another common error was to state that the ‘driver’s reaction time decreases’.
(b) Virtually all candidates understood the idea that a fair test was required to choose the best barrier to slow a car and not break. However few were able to explain how a change of the three different variables would affect the outcome and prevent a valid set of results being produced, that would provide evidence to which crash barrier was the best of the three under trial.
(c) Just over four fifths of candidates chose the correct answer.
E27. (a) (i) Most candidates were aware that the lorry would have the greatest momentum by reason of its greater mass. Vague responses, such as‘the lorry is bigger’, did not gain a mark. Some candidates took advantage of the relevant equation printed on the same page and calculated the momentum of the three vehicles. Incorrect responses generally involved the motorbike and indicated that the candidates were confusing momentum with the ability of the motorbike to accelerate faster than the other two.
(ii) This part question was generally answered well by those candidates with access to calculators. Candidates should be encouraged to check their calculations carefully as there were a number of instances of errors occurring in the transfer of the numbers from the question stem to the lines provided, to show their method of calculating the momentum of the motorbike.
(b) (i)&(ii)Just over nine tenths of candidates correctly answered that the kinetic energy would increase but they had less success in giving an appropriate reason. Most of the incorrect responses were in terms of the motorbike accelerating which had been stated in the part question stem. There were also many vague responses involving changes of force, power, friction, engine efficiency, etc.
(iii) Just over three quarters of candidates gained all three marks. Those that did not often drew a diagonal line from (4, 14) up to 20 m/s on the y-axis but the lines did not hit (6, 20) and were not subsequently continued horizontally to 8 s on the x-axis.
E28. (a) It was surprising that only a quarter of the candidates correctly answered ‘direction’ with ‘velocity in m/s’ a very common response. A small minority of candidates did not attempt this part question. It may be that many of these candidates did not look at the page carefully enough to realise there was a question at the top.
(b) Generally this question was well answered by the majority of students, with just over two-thirds scoring full marks. However, a large minority of students couldn’t substitute values from the text into a given equation correctly, often confusing time and speed. Some candidates didn.t recognise that the standard unit for mass is the kg and needlessly changed mass from kg into g, losing marks.
(c) Many candidates concentrated on the details of operation of airbags rather than the explanation of how they reduce risk of injury. There was little mention of ‘momentum’ from many candidates, and over two-fifths scored zero. Some candidates answered in terms of conservation of momentum, indicating that they had learned some physics but were not aware when to apply it. Of those that did give creditworthy answers there was often confusion over ‘reducing momentum’ and ‘reducing the rate of change of momentum’.
E29. (a) (i) This part question was answered very well with a large majority of candidates scoring both marks. However for those candidates failing to score the marks the main problem seemed to be lack of a calculator, or incorrect use of a calculator, evidenced by the use of lengthy iterative processes or missing zeros in their final answer.
(ii) Only a small minority of candidates were aware that the momentum of the vehicles were conserved in the collision, the most incorrect common response being that the momentum had decreased to zero.
(iii) Most candidates failed to appreciate that a stationary car has less momentum than a moving car.
(b) Just over half of the candidates scored both marks.
E30. (a) About two thirds of students scored this mark, showing that they had learnt that momentum has direction. A significant number of students ignored the information given in the question and stated that the two teenagers had different speeds or different mass.
(b) (i) Over two fifths of students scored this mark, giving a clear statement explaining momentum conservation, e.g. ‘momentum before = momentum after’ with many giving atextbook answer including the proviso that no external forces act. Some students suggested that the momentum was used up or ran out, or gave poor answers aboutforces and energy. Some students attempted to apply the rule to the particular case of the skateboard, explaining about the teenager and the boy having equal and/or opposite momenta. Unfortunately they generally did not go on to say that the (total) momentum had not changed.
(ii) Over two fifths of the students showed an excellent understanding of momentum conservation and presented clear working leading to a correct three mark answer. Another two fifths of students gained no marks at all. Their working showed little grasp of the mathematical aspects of momentum. There were many different wrong answers, the most common being 10/0.4 = 25, with no mass values involved at all. Of the remaining students, most gained a single mark for calculating the teenager’s momentum. Very few students obtained the second compensation mark by either stating the conservation of momentum or giving a numerical expression of this.
(c) Many students showed misconceptions about ‘force’ and ‘energy’, e.g. stating that without a force pushing it the board no longer has any energy, that it needs a force to keep it moving, or that friction is stronger than the kinetic energy. Very few connected friction with the work done against it. Too many wrong answers were comparing this question with question (b) and mentioning an increasing frictional force. As a result about two thirds of students did not score on this question. On the other hand, a few students showed clear understanding of the key terms and gained both marks for saying that kinetic energy is transferred as heat because of the friction force. About a third of students gained a single mark, usually for correctly referring to a friction force or, less often, for stating that kinetic energy is transferred by heating.
E31. (a) It was disappointing that only just over half of students could identify mass and speed as the factors that affect kinetic energy.
(b) (i) This was well answered by nearly all students. Most students recognised that because A was stationary or not moving that there would be no momentum.
(ii) This was correctly answered by nearly all students, with most correctly writing down the numerical values of mass and velocity before completing the multiplication.
E32. (a) A large majority of students (85%) scored full marks demonstrating an ability to use the given equation correctly. About 3% of students were able to substitute the values correctly into the equation but then made mistakes with the arithmetic. Approximately 12% of students were unable to correctly substitute values; often using v instead of v2
(b) (i) While most students were able to calculate a momentum using the given equation only about 23% of students recognised that they needed to find the difference between the initial and final momenta. Very few correctly calculated the change in velocity to be 60m/s to gain the compensation mark. Most of the 75% of students who scored zero on this part question only calculated the final momentum, albeit correctly, but unfortunately this was not creditworthy in the context of this question. Some students who did recognise that a change in momentum needed to be calculated confused signs and ended up with a change in momentum of zero thus demonstrating a lack of understanding of the concept.
(ii) Of the 23% of students that answered part (b)(i) correctly only a small number then made errors in this question. The vast majority of students managed to substitute their answer to (b)(i) into the equation for force and calculate the answer correctly, gaining an ‘error carried forward’ mark. Approximately half of the students who failed to score here did so because their answers to part (b)(i) were zero, making it impossible to gain this mark. There were a few students who at this stage realised that their answer of zero earlier must be incorrect so they deleted the calculation that resulted in a force of zero and came up with the correct figures, but failed to amend (b)(i) to match. Just over 83% of students scored this mark.
(c) Just over half of the students gained some credit on this question but only 28% scored both marks. Of these about half gained the marks by correctly stating that ‘the rate of change of momentum had decreased’. Other students were less concise but did tie-up increased time to the change in momentum. Of the students who did not score fully on this part question many offered confused statements, that the change in momentum was smaller, not realising that it is the same change in momentum to bring the ball to a stop or offered vague statements about the time taken slowing down.
E33. (a) Nearly 60% of students scored all three marks. However, “standing still” or “stationary” was a common wrong answer to A, even though the students were told the car was moving. Often, in B and C, students calculated the resultant force and did not describe the motion, just the direction; forwards for B or backwards for C.
(b) (i) Most students correctly gave the distance travelled while braking. Some students correctly wrote about the distance travelled after braking, or distance travelled in the braking time. A common wrong answer was to involve total distance travelled before the car stops, since this would include the reaction time. Many students lost the mark by putting a list of “braking and stopping distance”.
(ii) Only 25% of students scored this mark. Students often wrote about factors affecting stopping and braking distance; ‘bad weather conditions’ was a very common wrong answer. Also tiredness, being drunk, condition of road and state of vehicle were often given.
(c) (i) This mark was for giving both 5000 N and a clear direction. A lack of a simple arrow drawn in the correct direction kept many students from gaining this mark. Some students simply wrote ‘a very large force’ rather than quantifying it. A common incorrect answer was “5000 N on the car”. One of the most common responses was “5000 N towards the car”, which gained credit. Some students failed to include 5000 N in their answer, just stating that the resultant force was equal and opposite.
(ii) This question is about a dummy being used to measure/record the effects of impact/force. Many students wrote around this answer. “To see the force” was a common incorrect answer. Many students answered in terms of how much damage the dummy received, not mentioning measurement of the forces causing the damage and many students wrote about “impact”, instead of “force”, and did not gain credit for their answer.
(iii) A great number of students knew how to find the gradient of a velocity-time graph in order to calculate the acceleration, However, they failed to use only the straight line part of the graph - between 2 and 4 seconds. As a result, 10/4 was a common answer, giving 2.5 instead of 4. Often, the unit was the only credit-worthy part of an answer, although there were a number of mps, mph, km/s, etc. An answer of 40 was also quite common, multiplying 10 by 4. About half the students gave the correct unit; although m/s was a common incorrect answer. Some students drew a triangle correctly, but failed to use it, gaining one mark only. Some students correctly found 2 and 8, or 1 and 4, but then didn’t know how to calculate the acceleration; obtaining 16 or 0.25.
E34. (a) Just over 67% of students scored all three marks. A further 25% scored two marks. The most common error was to identify car A as being stationary, this was despite the word ‘moving’ being in bold in the stem of the question.
(b) (i) Nearly 90% of students scored this mark.
(ii) Just over 90% of students scored this mark.
(iii) This was not so well answered, with only 43% of students realising that the forces would be equal.
(iv) The majority of students (92%) realised the reason for attaching the sensors to the dummy.
E35. (a) Just over 67% of students scored all three marks. A further 25% scored two marks. The most common error was to identify car A as being stationary, this was despite the word ‘moving’ being in bold in the stem of the question.
(b) (i) Nearly 90% of students scored this mark.
(ii) Just over 90% of students scored this mark.
(iii) This was not so well answered, with only 43% of students realising that the forces would be equal.
(iv) The majority of students (92%) realised the reason for attaching the sensors to the dummy.
