A ball with a mass of 5 kg is rolling at 6 m/s and elastically collides with a resting ball with a mass of 3 kg. What are the post-collision velocities of the balls?

1 Answer
Apr 17, 2016

color(red)(v_1^'=3/2 m/s)
color(red)(v_2^'=15/2)

Explanation:

"momentums before collision"
P_1=m_2*v_1=5*6=30" " kg*m/s
P_2=m_2*v_2=3*0=0
Sigma vec P_b=vecP_1+vec P_2" total momentum before collision"

Sigma vec P_b=30+0=30 " "kg*m/s

"total momentum after collision must be "30 " "kg.m/s

"momentums after collision"
vec P_1^'=m_1*v_1^'=5*v_1^'
vec P_2^'=m_2*v_2^'=3*v_2^'

Sigma P_a=vec P_1^'+vec P_2^'
Sigma P_a=5*v_1^'+3*v_2^'

Sigma vec P_b=Sigma vec P_a

30=5*v_1^'+3*v_2^'" "(1)"

v_1+v_1^'=v_2+v_2^'
6+v_1^'=0+v_2^'
v_2^'=6+v_1^'" (2)"

"use the equation (1)"

30=5v_1^'+3(6+v_1^')
30=5v_1^'+18+3v_1^'
30-18=8v_1^'
12=8v_1^2
v_1^'=12/8
color(red)(v_1^'=3/2 m/s)

"use (2)"
v_2^'=6+v_1^'
v_2^'=6+1,5

color(red)(v_2^'=15/2)