1. A running back with a mass of 98 kg and a velocity of 7 m/s (toward the right

Question

1. A running back with a mass of 98 kg and a velocity of 7 m/s (toward the right) collides with, and is held by, a 147-kg defensive tackle going in the opposite direction (toward the left).
What is the velocity of the tackle before the collision for their velocity afterward to be zero? (Remember, velocity is a vector)


2. An elevator is able to raise 9,800 N to a height of 37 m in 12 s.
(a) How much work does the elevator do?


(b) What is the elevator's power output?


3. It takes 120 minutes for a middle-aged physics professor to ride his bicycle up the road to Alpe d'Huez in France.
The vertical height of the climb is 1,120 m, and the combined mass of the rider and bicycle is 73 kg. What is the bicyclist's average power output?

Explanation / Answer

1) by conservation of momentum , m1v1 + m2v2 = 0 => 98*7 + 147 *v2 = 0

=> v2 = - 98 * 7 / 147 = -4.67 m/s

2) a) work done = force * distance = 9800 * 37 = 362600 joules = 362.600 kJ

b) power output = work done / time = 362.600 / 12 = 30.21667 KW

3) power output = force * distance / time = 73 * 9.8 * 1120 / (120*60) = 111.284 W

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