Practice Problems (Momentum and Collisions)
1. You throw a piece of bread into a lake full of birds. A 9 kg Canadian goose (coming from the south
at 1.3 m/s), a 4 kg duck (coming from the West at 1.1 m/s), and a 4 kg seagull (coming from the
North at 1.1 m/s) race towards the bread. What is the total momentum of the three birds?
2. Two football players run towards each other along a straight path. The 1st player is 95 kg and runs
towards the 2nd player at 3.75 m/s. The 2nd player is 111 kg and moves towards the 1st player at
4.10 m/s. They end up in a head-on collision and are stuck together. (a) What is their velocity
immediately after the collision? (b) What are the initial and final kinetic energies of the system?
3. Two cars collide at an orthogonal intersection. rrom a top-view of this intersection, the first car is
950 kg and has a speed of 16 m/s approaching from the left. The second car is 1300 kg and has a
speed of 21 m/s approaching from below. They collide and stick together. rind the speed and
direction of the vehicles just after the collision. Assume there are no external forces.
4. Two astronauts decide to toss fruit at each other. Astronaut 1 throws a 0.13 kg apple towards
Astronaut 2 (right) with a speed of 1.11 m/s. Meanwhile, Astronaut 2 throws a 0.16 kg orange
towards Astronaut 1 (left) with a speed of 1.21 m/s. The fruits collide, sending the orange off with
a speed of 1.16 m/s at an angle of 42° below its original direction of motion. rind the final speed
and direction (assume it is above its original direction of motion) of the apple. Assume an elastic
collision.
5. In a ballistic pendulum, a bullet of mass 𝑚� is fired with an initial speed at a wooden block hanging
from a massless string of length 𝐿�. The wooden block has a mass of 𝑀�. After the collision, the
bullet is embedded into the wooden block, and together as one, they swing through an arc,
eventually gaining a peak height of ℎ. rind an expression for the height ℎ and the angle 𝜃� the
string makes to its original position at peak height.