A ball with a mass of #5 kg# moving at #8 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?

Question

1221 views around the world

You can reuse this answer
Creative Commons License

Answer 1 · 2017-12-20T14:38:56

The velocity of the second ball is #=1.905ms^-1# and the energy lost is #=121.9J#

#m_1u_1+m_2u_2=m_1v_1+m_2v_2#

The mass #m_1=5kg#

The mass #m_2=21kg#

The velocity of the first ball is #u_1=8ms^-1#

The velocity of the second ball is #=v_1ms^-1#

Therefore,

#5*8+21*0=5*0+21*v_2#

#40+0=0+21v_2#

#v_2=40/21=1.905ms^-1#

The kinetic energy before the collision is

#KE_1=1/2m_1u_1^2=1/2*5*8^2=160J#

The kinetic energy after the collision is

#KE_2=1/2m_2v_2^2=1/2*21*(40/21)^2=38.1J#

The energy lost as heat is

#DeltaKE=KE_1-KE_2=160-38.1=121.9J#