11. Momentum & Impulse

Push-Away Problems

Multiple Choice
An 80-kg astronaut is stranded floating in space is 30 m away from his spaceship. He wants to return to his spaceship in 20 s. How fast must he throw his 2-kg space hammer, directly away from the spaceship, to accomplish this?
Open Question
(II) A 0.145-kg baseball pitched horizontally at 35.0 m/s strikes a bat and pops straight up to a height of 31.5 m. If the contact time between bat and ball is 2.5 ms, calculate the average force between the ball and bat during contact.
Open Question
A 1000 kg cart is rolling to the right at 5.0 m/s . A 70 kg man is standing on the right end of the cart. What is the speed of the cart if the man suddenly starts running to the left with a speed of 10 m/s relative to the cart?
Open Question
INT A 1500 kg weather rocket accelerates upward at 10 m/s² . It explodes 2.0 s after liftoff and breaks into two fragments, one twice as massive as the other. Photos reveal that the lighter fragment traveled straight up and reached a maximum height of 530 m. What were the speed and direction of the heavier fragment just after the explosion?
Open Question
An object at rest explodes into three fragments. FIGURE EX11.32 shows the momentum vectors of two of the fragments. What is the momentum of the third fragment? Write your answer using unit vectors.
Open Question
A 45 g projectile explodes into three pieces: a 20 g piece with velocity 25î m/s , a15 g piece with velocity −10î+10ĵ m/s , and a 10 g piece with velocity −15î−20ĵ m/s . What was the projectile's velocity just before the explosion?
Open Question
A 30 ton rail car and a 90 ton rail car, initially at rest, are connected together with a giant but massless compressed spring between them. When released, the 30 ton car is pushed away at a speed of 4.0 m/s relative to the 90 ton car. What is the speed of the 30 ton car relative to the ground?
Open Question
Dan is gliding on his skateboard at 4.0 m/s. He suddenly jumps backward off the skateboard, kicking the skateboard forward at 8.0 m/s. How fast is Dan going as his feet hit the ground? Dan's mass is 50 kg and the skateboard's mass is 5.0 kg.
Open Question
(II) The force on a bullet along the barrel of a firearm is given by the formula F = [740 ― (2.3 x 10⁵ s⁻¹ ) t] N over the time interval t = 0 to t = 3.0 x 10⁻³ s .
(e) What is the recoil speed of the 4.5-kg gun?
Open Question
(III) A 360-kg four-wheel flat cart 15 m long is moving horizontally with a speed of 6.0 m/s. A 110-kg worker starts walking from one end of the cart to the other in the direction of motion, with speed 2.0 m/s with respect to the cart. In the time it takes for him to reach the other end, how far has the cart moved?