U1.3 Collisions, explosions and impulse

Question 1

What is momentum?

Answer 1

The product of a moving object’s velocity and mass

Question 2

What does the law of conservation of momentum state?

Answer 2

When two objects collide the total momentum before the collision is equal to the total momentum after the collision (in the absence of external forces). This is true for all collisions

Question 3

When is kinetic energy not conserved?

Answer 3

In inelastic collisions

Question 4

When is kinetic energy conserved?

Answer 4

In elastic collisions

Question 5

What is impulse?

Answer 5

The product of average force and time of contact for a collision… The change in momentum

Question 6

State Newton’s third law.

Answer 6

Every action force has an equal and opposite reaction force

Question 7

What is the area under a force time graph equal to?

Answer 7

Impulse

Question 8

Modern cars are designed to crumple on impact in a collision. How does this help to protect the occupants from harm?

Answer 8

The change in momentum (area under the force time graph) can’t be changed at the time of the accident (mass is fixed and it is too late for the driver to slow down). Crumpling on impact increases the time of collision. This means the peak force is less and hopefully lets the occupants come to less harm as a result.