Physics 100
Conservation of Momentum
Collisions Class Work
Assume that the sum of any external forces acting on the system is zero. Note: The arrows are
just supposed to show the direction of the car’s movement. They do not represent the magnitude
of the velocity.
1) Find the final velocity of the car on the right hand side.
Before the
V = 2 m/s
collision
V = -2 m/s
1 kg
After the
collision
2 kg
V= ?
V = -1 m/s
1 kg
2 kg
2) After the collision, the two cars stick together. Find the final velocity of the two cars.
Before the
V = 2 m/s
V=0
collision
1 kg
2 kg
After the
collision
V= ?
1 kg
2 kg
3) After the collision, the two cars stick together. Find the initial velocity of the car on the right
hand side.
Before the
V = 3 m/s
collision
V= ?
1 kg
1 kg
After the
collision
V = 2 m/s
1 kg
1 kg
4) Two carts are at rest with a spring in between them. The spring is released. Find the mass of
the cart on the right hand side.
Before the
spring is
V = 0 m/s
released
2 kg
After the
spring is
released
V = -2 m/s
2 kg
? kg
V = 0.5 m/s
? kg
5) A cart is moving at a constant speed when a frog falls straight down onto the cart and sticks.
The frog had no horizontal velocity before landing in the cart.
Before the
Frog
V = 3 m/s
frog falls
onto the cart
1 kg
After the frog
falls onto the
cart
Frog
V= ?
1 kg
mfrog = 0.5 kg
a) Find the velocity of the cart and frog.
b) The frog then decides to jump straight up to a branch. What is the speed of the cart after the
frog jumps up?
Collisions Homework
Elastic Collisions – Remember momentum is always conserved!
1. Cart A moves towards Cart B. Both hit and then move in opposite directions. The mass
of cart A = 2.00kg, its velocity was 3.00m/s, it’s velocity after the collision is -2.00m/s.
The mass of cart B = 4.00kg, its velocity is -1.00m/s. What is cart B’s velocity after the
collision?
2. Rocky has a mass of 85kg and is moving at 10m/s toward Jennifer who has a mass of
60kg and is moving at -20m/s. They collide and then move in opposite directions.
Rocky is now moving at -5m/s. What is Jennifer’s velocity after the collision? Is it
positive or negative? (Assume they keep their balance).
3. A VW bug moving at 40m/s collides with a truck with a mass of 700kg moving at 30m/s. They collide and move in separate directions. The truck has a velocity of 25m/s
after the collision and the VW bug is moving at -35m/s. What is the mass of the VW
bug?
Inelastic collisions
4. Cart A has a mass of 2.00kg and a velocity of 3.00m/s. Cart B has a mass of 4.00 kg and
a velocity of -1.00m/s. They collide but DO NOT separate. What is their velocity after
the collision?
5. A mini with a mass of 250kg is moving at a velocity of 60 m/s. It collides with a Mack
truck that has a mass of 2000kg and a velocity of -30m/s. They collide but DO NOT
separate. What is their velocity after their collision?
6. Rocky has a mass of 85kg and is moving at 10m/s toward Jennifer who has a mass of
60kg and is moving at -20m/s. They collide but DO NOT separate. What is their
velocity after the collision? (Assume they keep their balance).