Physics Chapter 7

A 2-kg blob of putty moving at 3 m/s slams into a 2 kg blob of putty at rest A) Calculate the speed of the two stuck together blobs of putty immediately after colliding B) Calculate the speed of the two blobs if the one at rest was 4 kg

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Why is the Pelton Wheel an improvement over paddle wheels with flat blades?

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Distinguish between impact and impulse. Which designates a force and which is force multiplied by time?

-Impact= force -impulse= force times time

distinguish between mass and momentum. Which is inertia and which is inertia in motion?

-Mass is ineritia -momentum is inertia in motion

In a car crash, why is it advantageous for an occupant to extend the time during which the collision takes place?

-bc it would decrease the force -more time = less force

Why is it advantageous for a boxer to ride with the punch? Why should he avoid moving into an oncoming punch?

-because more time = less force

Does impulse equal momentum, or a change in momentum?

-change in momentum

For a constant force, suppose the duration of impact (time) on an object is doubled. How much is the impulse increased? How much is the resulting change in momentum (impulse) increased?

-double -double

Imagine that you are hovering next to the space shuttle in an Earth orbit. Your buddy of equal mass, who is moving at 4km/h with respect to the shuttle, bumps into you. If he holds onto you, how fast do you both move with respect to the ship?

-double mass moves it half the speed -2km/h

Distinguish between an elastic and an inelastic collision

-elastic bounces; inelastic sticks, also generates heat

Which has the greater mass, a heavy truck at rest or a rolling skateboard? Which has a greater momentum?

-heavy truck at rest -skateboard has greater momentum bc it is moving

Distinguish between impulse and momentum. Which is force times time and which is inertia in motion?

-impulse= force times time -momentum= inertia in motion

When the force of impact on an object is extended in time, does the impulse increase or decrease?

-increase if time increases the impulse increases

If the time of impact in a collision is extended by four times, how much does the force of impact change?

-it is divided by 1/4

Why is more impulse delivered during a collision when bouncing occurs than during one when it doesn't?

-momentum change would be more

What does it mean to say that momentum is conserved?

-the amount before the collision is the same amount as after -momentum stays the same

In terms of momentum conservation, why does a cannon recoil when fired?

-the guns momentum has to be equal and opposite to the bullet

Is momentum conserved for colliding objects that are moving at angles to one another?

-yes; there is vector and it follows vector rules

A) what impulse occurs when an average force of 10 N is exerted on a cart for 2.5s? B) what change in momentum does the cart undergo? C) If the mass of the cart is 2 kg and the cart is initially at rest, calculate the final speed

A) 10 x 2.5 25 N s B) 25 N s C) 25/2 12.5 m/s

A) what is the momentum of a 50kg carton that slides at 4m/s across an icy surface? B)the sliding carton skids onto a rough surface and stops in 3s. Calculate the force of the friction it encounters.

A) 50 x 4 200 N s B) 200/3 66.7 N

A) what is the momentum of an 8kg bowling ball rolling at 2m/s? B) if the bowling ball rolls into a pillow and stops in 0.5s, calculate the average force it exerts on the pillow C) what average force does the pillow exert on the ball?

A) P= 8 times 2 P= 16 kg m/s or N s B) 16/.5 = 32N C) 0 N s

Visualize yourself on a skateboard A) when you throw a ball, do you experience an impulse? B) do you experience an impulse when you catch a ball of the same speed? C) do you experience an impulse when you catch it and then throw it out again? D) which impulse is greater?

A) yes B) yes C) yes D) catching it and then throwing it