Calculate the velocity of the joint mass.?

A mass of 120kg moves along a straight line at 7m/s. It collides with another mass of 175kg moving in the opposite direction at 4m/s on the same straight line. The two masses join together on collision; calculate the velocity of the joint mass.

some working out would be good as well

Answer:

 you can use momentum law:

m1*v1 + m2*v2 = m1*v1' + m2*v2'

because they join together, velocity is same, thus

m1*v1 + m2*v2 = m1*v'+m2*v'
m1*v1 + m2*v2 = (m1+m2)*v'
120*7+175*(-4)=(120+175)*v'
v'=0.47 m/s

so the velocity joint mass is 0.47 m/s