# Homework Help: Momentum and velocity at certain distance?

1. Oct 11, 2009

### MechaMZ

1. The problem statement, all variables and given/known data

For momentum, what should i determine the final velocity if there is a deceleration or acceleration? should i use the kinematic equation to determine the velocity in the case?

however, if i'm required to find momentum after the object is already traveled a certain distance?

Questions:
1. How fast can you set the Earth moving? In particular, when you jump straight up as high as you can, what is the maximum recoil speed that you give to the Earth? Let your mass be 70.0 kg and your maximum jump height be 0.500 m. Model the Earth as a perfectly solid object.

2. A ball of mass 0.100 kg is dropped from rest from a height of 1.25 m. It rebounds from the floor to reach a height of 0.840 m. What impulse was given to the ball by the floor?

how do i define the velocity for mv, because the velocity is not constant due to the gravitational force.

Last edited: Oct 11, 2009
2. Oct 11, 2009

### CompuChip

Momentum is simply mass times velocity. So if the mass doesn't change, you can calculate the change in momentum by the change of velocity.

However, this is probably not precisely the answer you are looking for... can't you just post the question you're working on? :)

3. Oct 11, 2009

### MechaMZ

Hi compuchip,

i'm currently working on this example, the one i posted in the first post.

1. How fast can you set the Earth moving? In particular, when you jump straight up as high as you can, what is the maximum recoil speed that you give to the Earth? Let your mass be 70.0 kg and your maximum jump height be 0.500 m. Model the Earth as a perfectly solid object.

2. A ball of mass 0.100 kg is dropped from rest from a height of 1.25 m. It rebounds from the floor to reach a height of 0.840 m. What impulse was given to the ball by the floor?

Last edited: Oct 11, 2009
4. Oct 12, 2009

### MechaMZ

should i consider the gravitational force as an internal force in the system?

5. Oct 13, 2009

### MechaMZ

could anyone give me some hints on these problems?

6. Oct 13, 2009

### lewando

1) You need to lookup the mass of the Earth. What would your initial velocity need to be in order to give you an altitude of 0.500 m?

2) What is the maximum velocity of the ball before it hits the ground?