Question

Two bodies of mass 40kg and 60kg are moving in opposite directions towards each other with velocities 40m/s and 30m/s respectively. They collide and move in opposite direction. If the velocity of first body after collision is 25m/s,then what will be the velocity of the second body?

Answer 1

m1u1+m2u2 = m1v1+m2v2
40(40)+60(-30) = 40(25) + 60(v2)
1600-1800 = 1000+60v2
-200-1000 = 60v2
-1200/60 = v2
-20m/s = v2
negative sign denotes body is moving in opposite direction
hope this helps

Answer 2

Answer:

13.33 m/s

Explanation:

Let the two bodies be known as A and B. Then, we have :-

(i) mass(A) = 40 kg ; initial velocity(A) = 40m/s

Momentum(p1) = mass(A)*velocity(A)

                       = 40 kg * 40 m/s

                       = 1600 kg*m/s

(ii) Taking the direction of velocity as negetive,  we get :-

 mass(B) = 60 kg ; initial velocity(B) = -30m/s

 Momentum(p2) = mass(B)*velocity(B)

                          = 60 kg * -30 m/s

                          = -1800 kg*m/s

Now, it is given that after collision the velocity of A is 25m/s.

    m(A)*u(A) - m(B)*u(B) = -m(A)*v(A) + m(B)*v(B)

⇒  40*40 - 60*30 = -40*25 + 60*v(B)

⇒  v(B) = 13.33 m/s.