# Homework Help: Collision:child jumps on moving cart, cart slows down, find mass of the cart, impulse

1. Nov 11, 2009

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

A cart is driving on straight tracks with a velocity of 2 m/s. In the opposite direction, with an angle of 60º according to the tracks, a child with a mass of 2 kg is running with a velocity of 2m/s, he jumps on the cart and stays there.
- Find the mass of the cart, if its velocity is reduced to 1 m/s when the child jumps onto it.
- What is the impact force perpendicular to the tracks?

http://www.slide.com/s/QOXg7ix_pD-d7WoZA5-k0knIny1R-ZsX?referrer=hlnk [Broken]

2. Relevant equations

p= mv
F= ma

3. The attempt at a solution

First part: Find the mass of the cart, if its velocity is reduced to 1 m/s when the child jumps onto it.

Conservation of the moment:

m(2)= 20 kg, v(1-initial)= v(2-initial)= 2 m/s, v(3)= 1 m/s, θ= 60º

m(1)v(1) + m(2)v(2)sinθ= (m(1) + m(2))v(3)
2m(1) + 34.64= m(1) + 20
m(1)= 14.64 kg

Are my calculations correct?

Second part: What is the impact force perpendicular to the tracks?

For this part, I know that the formula for impact force is F(impact)=m(Δv/Δt), but I don't know which mass to use and I don't have the time (t).
Any hint what I should do, or is there another equation to find the impact force without knowing the time (t)?

Thank you for helping!

Last edited by a moderator: May 4, 2017
2. Nov 11, 2009