Unit 9 Worksheet 2 Guide
1. Initially, the bullet and gun are not moving. The final situation is the gun moving back a little bit, and the bullet moving
very, very fast. Use the conservation of momentum, and solve for the final velocity of the gun.
2. When the girl holds the gun tightly, it’s as if the gun and girl is one object. This would make the gun’s mass 50kg.
3. Initially, the empty car is moving and the full car is not moving. In the final situation, both cars hook together as if they
were one object and move off together. So in the final situation, you should have both masses added together
multiplied by the final velocity of both cars. Solve for the final velocity of both cars.
4. Initially, the astronaut and tank are not moving. The final situation is the astronaut moving back (left) and the tank
moving forward (right). Use the conservation of momentum, and solve for the final velocity of the astronaut.
5. Since both the given velocities are positive, and the situation is someone returning a serve, then one of those has to
be negative. I chose the 30m/s serve as positive (moving right) and the return 25m/s moving to the left. Use Ft = mΔv
and solve for force.
6a. Use J = Δp  J = pf – pi This will be the impulse the cart gives to the boy, so the positive value is the impulse the
boy gives to the cart.
6b. Conservation of momentum where initially the boy and cart’s mass should be added together and multiplied by the
velocity of both (2m/s). In the final situation, the momentum of the boy is zero. Solve for the final velocity of the cart.
7. This is very similar to #1 & #4, but after you find the final velocity of the larger girl, now find the impulse given to both.
8. Conservation of momentum where initially the melon is not moving, but after the arrow goes through the melon is
moving a little bit.
9. Conservation of momentum. When you plug in values, remember to make one of the initial velocities negative
because they are running in opposite directions.