A common action movie stunt involves the hero jumping from a deck or a ledge dow

Question

A common action movie stunt involves the hero jumping from a deck or a ledge down into a moving convertible. Consider the following situation: James Bond (mass= 87Kg) and the enigmatic spy Jinx (mass=69Kg) are trying to stop a runaway convertible as it emerges from a parking garage by jumping into it from the deck immediately above the exit. Timing their leaps perfectly, and synchronized perfectly with each other, they drop into the seat of the moving car (mass=950Kg). The car is in neutral, and its speed just before they hit the seat is 10.4 m/s. When Bond and Jinx land in the car, it slows to 9.6 m/s.

A) As they hit the car they are carrying forward momentum (from running) as well as vertical momentum (from gravity). In order to treat this as a conversation of momentum problem, what must constitute the "closed system?" Explain.

B) With what speed must Bond and Jinx have been running (horizontally) in order for the final speed of the car, including passengers, to be 9.6 m/s? Assume that there are no frictional losses in the horizontal direction.

Explanation / Answer

1. closed system would consist of the momentum of the van and the actors included in x direction and no normal forces to be considered
2. m1v1 + m2v2 + Mv3 = (m1 + m2 + M)V [ from momentum conservation]
(87+69)u + 950*10.4 = (87+69+950)*9.6
u = 4.7282 m/s

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