Question

A ball with a mass of `2 kg` moving at `16 m/s` hits a still ball with a mass of `21 kg`. If the first ball stops moving, how fast is the second ball moving? How much kinetic energy was lost as heat in the collision?

Answer 1

In the first scenario, momentum conservation law will be applied.

Explanation:

from the law,
`m_1u_1+m_2u_2=m_1v_1+m_2v_2`

here,
`m_1=2kg`
`m_2=21kg`
`u_1=16ms^(-1)`
`u_2=0ms^(-1)`
`v_1=0ms^(-1)`
we have to find `v_2`
if we put all the values in the equation, we will find,

`2*16+21*0=2*0+21*v_2`
`or, 32=21v_2`
`or, v_2=32/21`
`or, v_2=1.524ms^(-1)`

for the energy loss,
`E_(i)=1/2*2*16^2+1/2*21*0^2`
`=256j`

`E_(f)=1/2*2*0^2+1/2*21*1.524^2`
`=24.387j`

so, `Delta E=E_(i)-E_f`
`=256j-24.387j`
`=231.613j`