Question

Two railway trucks of masses m and 3m move towards each other in opposite directions with speeds 2v and v respectively. These trucks collide and stick together.

What is the speed of the trucks after the collision?
A
v/4
B
v/2
C
v
D
5v/4

Answer 1

Answer: The correct answer is -v/4.

Step-by-step explanation:

By applying equation of collision.

m1u1 + m2u2 = v(m1+m2).

The second object is moving in opposite direction so its momentum is negative. So, we have.

V= m1u1 + (-m2u2)/ m1 + m2

By imputing the data we have;

V = m×2v + (-3m×v)/ m+3m

V= 2mv - 3mv/ 4m

V = -mV/4m

V= -v/4//

NB: we have negative V because m2 is bigger than m1.