34. REASONING AND SOLUTION Momentum is conserved in the horizontal direction during the "collision." Let the coal be object 1 and the car be object 2. Then
The direction of the final velocity is to the right .
39. SSM REASONING The two balls constitute the system. The tension in the wire is the only nonconservative force that acts on the ball. The tension does no work since it is perpendicular to the displacement of the ball. Since Wnc = 0 J, the principle of conservation of mechanical energy holds and can be used to find the speed of the 1.50-kg ball just before the collision. Momentum is conserved during the collision, so the principle of conservation of momentum can be used to find the velocities of both balls just after the collision. Once the collision has occurred, energy conservation can be used to determine how high each ball rises.
SOLUTION
a. Applying the principle of energy conservation to the 1.50-kg ball, we have
If we measure the heights from the lowest point in the swing, hf = 0 m, and the expression
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