lesson #12

• 2nd big conservation law in Physics (after Conservation of Energy)

• The total momentum of a system of objects remains constant.

• Very useful in observing collisions and explosions.

• momentum is mass times velocity, indication of how hard it is to stop an object

• Impulse is force times time; Impulse is also equal to change in momentum.

• Individual objects change momentum any time there is a net force, but the total amount of momentum does not change.

• Momentum and Impulse will be useful in analyzing collision problems

1. A 0.5 kg ball is moving east at a speed of 2 m/s. Calculate the momentum of the ball.

2. A shopping cart with a mass of 10 kg is pushed and reaches a speed of 1.5 m/s in 2 seconds. If the applied force is constant, what is the impulse delivered to the cart?

3. A 0.8 kg ball is suspended from a string. A 0.05 kg projectile hits it horizontally at a speed of 400 m/s and becomes embedded in the ball. Calculate the impulse imparted to the ball and the final momentum of the ball-projectile system.
4. Two skaters, one of 50 kg and another of 60 kg, are standing on ice and push each other. If the 50 kg skater moves backward at 2 m/s, at what speed will the 60 kg skater move?

5. A 1500 kg car is parked and is hit by another car of 1000 kg moving at 10 m/s. If after the collision they move together, at what speed will they do so?
6. A 2000 kg railway wagon moving at 4 m/s collides and couples with another wagon of 3000 kg which is initially at rest. Find the speed of the combined wagons after the collision.