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?

In order to solve this question we need to use the principle of conservation of momentum which states:

The momentum in a closed system remains constant before and after a collision or explosion.

I.E.

momentum before=momentum after

And ingeneral momentum is calculated using: P=mv where P is the momentum, m is the mass of the object, and v is the velocity of the object.

Hence the total momentum before the collision is:

P1+P2

=m x 2v + 3m x -v       NOTE: notice the negative v on the second truck as it is moving in the opposite direction to the first truck

=-mv

After the collision the the trucks stick together so the total mass becomes 4m and the combined trucks move at an unknown speed of v​after

We will solve the equation for conservation of momentum to determine vafter​:

mv=4mvafter

cancelling out the m's:

v=4vafter

and rearranging to make v​after the subject of the equation:

vafter​=0.25v

Which is our final answer.

SW
Answered by Sarah W. Physics tutor

34510 Views

See similar Physics A Level tutors

Related Physics A Level answers

All answers ▸

What is the standard model?


How can I describe the motion of an object falling, due to gravity, through a fluid? And when does the object reach terminal velocity?


An object with weight w is suspended from two strings at angles θ1 and θ2 to the vertical and with tensions T1 and T2. How would you resolve the vertical and horizontal forces?


How would I derive Kepler's third law from Newton's law of gravitation and the equations of circular motion?


We're here to help

contact us iconContact ustelephone icon+44 (0) 203 773 6020
Facebook logoInstagram logoLinkedIn logo

MyTutor is part of the IXL family of brands:

© 2025 by IXL Learning