A ball with a mass of #2 kg# moving at #14 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?

1 Answer
Feb 22, 2016

The speed of the second ball is #1.3m/s#
The kinetic energy lost in as heat was #177.3J#

Explanation:

The momentum is conserved, then

#p_1 = m_1*v_1 = p_2 = m_2*v_2#

#v_2 = v_1*m_1/m_2# and replacing for the problems figures
#v_2 = 14m/s*2/21 = 1.3m/s#

The energy also is conserved

#E= m_1*v_1^2/2 = m_2*v_2^2/2 + Q# where Q is the kinetic energy

lost in the impact, then

#Q = m_1*v_1^2/2*[1-m_1/m_2]# and replacing for the problems figures

#Q= 2/2kg*14^2 m^2/s^2*[1-2/21]=177.3J#