Impulse and Momentum

Impulse and Momentum

Momentum

Impulse

F vs. t graphs

Because impulse is the product of the sum of the forces and time interval, impulse is the area under a F vs. t graph.

Because this is not a calculus based class, we will use average force, F_av, multiplied by time, shown as a square.

Multiple Choice

The cart’s change of momentum,

$$\Delta p_x$$ , is

• –20 kg m/s

• -10 kg m/s

• 0 kg m/s

• 10 kg m/s

• 30 kg m/s

Multiple Choice

A 2.0 kg object moving to the right with speed 0.50 m/s experiences the force shown. What are the object’s speed and direction after the force ends?

• 0.50 m/s left

• at rest

• 0.50 m/s right

• 1.0 m/s right

• 2.0 m/s right

Multiple Choice

A 2.0 kg object moving to the right with speed 0.50 m/s experiences the force shown. What are the object’s speed and direction after the force ends?

• 0.50 m/s left

• at rest

• 0.50 m/s right

• 1.0 m/s right

• 2.0 m/s right

Multiple Choice

A force pushes the cart for 1 s, starting from rest. To achieve the same speed with a force half as big, the force would need to push for

• 1/4 s

• 1/2 s

• 1 s

• 2 s

• 4 s

A couple of points worth emphasizing when dealing with impulse-momentum problems

• If the magnitude of the force changes during the time interval, use the average force.

• If the same force is exerted for the same time interval on a large-mass object and on a small-mass object, the objects will have an equal change in momentum (the same impulse was exerted on them)

Multiple Choice

A light plastic cart and a heavy steel cart are both pushed with the same force for 1.0 s, starting from rest. After the force is removed, the

momentum of the light plastic cart is ________ that of the heavy steel cart.

• greater than

• equal to

• less than

• can't say; depends on how big the force is

Multiple Choice

You awake in the night to find that your living room is on fire. Your one chance to save yourself is to throw something that will hit the back of your bedroom door and close it, giving you a few seconds to escape out the window. You happen to have both a sticky ball of clay and a super-bouncy Superball next to your bed, both the same size and same mass. You’ve only time to throw one. Which will it be? Your life depends on making the right choice!

• Throw the superball.

• Throw the ball of clay.

• It doesn't matter. Throw either.

Poll

Would you rather fight 10 duck-sized horses, or 1 horse-sized duck?

• 10 duck-sized horses

• 1 horse-sized duck

Multiple Choice

A mosquito and a truck have a head-on collision. Splat! Which has a larger change of momentum?

• the mosquito

• the truck

• they have the same change in momentum

• can't say without knowing their initial velocities

Having a hard time accepting the mosquito- truck answer? Let's analyze...

You gotta love physics!!!

Multiple Choice

The two boxes are on a frictionless surface. They had been sitting together at rest, but an explosion between them has

just pushed them apart. How fast is the 2-kg box going?

• 1 m/s

• 2 m/s

• 4 m/s

• 8 m/s

• not enough info given