Teacher Notes – Activity 1: Position–Match Graph
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DataSketch a graph for one run of velocity versus time. Include units and labels for your axes. (See Sample Data.) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Cart 1 |
Cart 2 |
Before |
After | ||
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Item |
Mass (kg) |
Mass (kg) |
Velocity, cart 1 (m/s) |
Velocity, cart 2 (m/s) |
Velocity, cart 1 (m/s) |
Velocity, cart 2 (m/s) |
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1 |
0.239 |
0.253 |
0.25 |
-0.41 |
-0.42 |
0.23 |
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Calculations
Calculate the total momentum before and the total momentum after for each collision.
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Item |
Momentum Before (kg•m/s) |
Momentum After (kg•m/s) |
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1 |
-0.0439 |
-0.0422 |
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Questions
In general, how does the momentum after a collision compare to the momentum before the collision?
Answers will vary. In general, the momentum after a collision will be close to–but probably less than–the momentum before the collision.
In which type of collision was the before-and-after difference in momentum the least? In which type of collision was the difference the most?
Answers will vary.
What factors might cause the total momentum after a collision to not equal the total momentum before the collision?
Friction, misalignment of the carts during collision, and uncertainty in the measurement of mass are some examples of factors that might cause the momentum after to not equal the momentum before.
For a theoretical head-on collision between two carts of equal mass and equal speed, what is the total momentum before the collision?
For a head-on collision between two carts of equal mass and equal speed, the total momentum before the collision is zero.
Discuss the momentum of a firecracker at rest compared to the momentum of the firecracker after it explodes.
The momentum of a firecracker at rest is zero. The momentum of all the fragments of the firecracker after it explodes is also zero.
Imagine two carts, one with twice the mass of the other, that are going to have a head-on collision. In order for the two carts to be at rest after the collision, how fast must the less massive cart move compared to the more massive cart?
For two carts to be at rest after collision, their total momentum before collision would be zero. For that to happen when one cart is half as massive as the other, it must have twice the speed of the more massive cart.
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