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

34063 Views

See similar Physics A Level tutors

Related Physics A Level answers

All answers ▸

A ball is thrown vertically downwards at a speed of 10ms^-1 from a height of 10m. Upon hitting the floor 10% of the energy is dissipated through waste heat. What is the heighest point the ball reaches before it comes to rest? Take g=10ms^-2


A car of mass 800 kg is accelerated horizontally by constant net force of 1920 N for 9 s. It then breaks for 2 s, but drives off a 5 m high cliff. If μ = 0.85, what is the total horizontal distance travelled by car and its velocity? Ignore air resistance.


What is the photoelectric effect?


Give examples of how the photoelectric effect supports the particle nature of light and defies the wave theory.


We're here to help

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

© MyTutorWeb Ltd 2013–2025

Terms & Conditions|Privacy Policy
Cookie Preferences