Physics Ch 07 Momentum

How do we define impulse?

• A force that is applied at random.

• A force that is applied only for a short period of time.

• Force multiplied by the time of impact

• The time interval that a force lasts.

The total momentum of a system is conserved

• always

• If no external forces act on the system.

• If no internal forces act on the system.

• Never; it’s just an approximation.

Tags

NGSS.HS-PS2-2

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 of momentum.

• Can’t say without knowing their initial velocities.

Answer explanation

They must have the same impulse. Impulse = force x time. They exert the same force on each other because of Newton's Third Law, and the time of contact must be the same for both. Since impulse is the same, the change in momentum must be the same.

Tags

NGSS.HS-PS2-2

A mosquito and a truck have a head-on collision. Splat! Which has a larger impulse applied to it?

• The mosquito

• The truck

• They have the same impulse.

• Can’t say without knowing their initial velocities.

Answer explanation

They must have the same impulse. Impulse = force x time. They exert the same force on each other because of Newton's Third Law, and the time of contact must be the same for both.

Tags

NGSS.HS-PS2-1

NGSS.HS-PS2-2

In order to catch a ball, a baseball player naturally moves their hand backward in the direction of the ball's motion once the ball contacts the hand. This habit causes the force of impact on the player's hand to be reduced in size mostly because _____

• a resulting impact velocity has lessened

• the momentum change is decreased

• the time of impact is increased

• the time of impact is decreased

• none of the above

Tags

NGSS.HS-PS2-3

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. It depends on how big the force is.

Answer explanation

Since they are pushed with the exact same force, and the amount of time they were pushed is the same, they must have had the same impulse applied to them. This means they must have the same change in momentum.

Tags

NGSS.HS-PS2-1

NGSS.HS-PS2-2

What is the total change in the cart's momentum?

• –20 kg m/s

• –10 kg m/s

• 0 kg m/s

• 10 kg m/s

• 30 kg m/s

Answer explanation

Δp = final momentum minus initial momentum. Final momentum = (10 kg)(+1 m/s) = +10 kg⋅m/s. Initial momentum = (10 kg)(-2 m/s) = -20 kg⋅m/s.

Tags

NGSS.HS-PS2-2

A 4 kg object has a momentum of 12 kg-m/s. The object's speed is ______ m/s

• 3

• 4

• 12

• 48

• none of these

Tags

NGSS.HS-PS2-2

A 5-N force is applied to a 3-kg ball to change its velocity from +9 m/s to +3 m/s. How much did the ball's momentum change?

• -2.5 kg m/s

• -6 kg m/s

• -18 kg m/s

• -45 kg m/s

Tags

NGSS.HS-PS2-1

A 5-N force is applied to a 3-kg ball to change its velocity from +9 m/s to +3 m/s. How much impulse did the ball experience?

• -2.5 N s

• -6 N s

• -18 N s

• -45 N s

Answer explanation

Impulse is equal to change in momentum. So figure out the final momentum and the initial momentum, and subtract them.

Tags

NGSS.HS-PS2-2