Conservation of momentum and energy: Self Test

A man drops a 10-kg rock from the top of a 5-meter ladder

Assuming that air friction is negligible, how much kinetic energy does it have when it hits the ground? Calculate the answer yourself if you can.

Hint: First Calculate the potential energy at the top

Potential energy at top = weight • height

Remember weight = mass • gravity = mg

PE = mg • height

PE = kg • m/s² • m
PE = (kg • m/s²) • m
PE = newton • m
PE = joules

What is the speed of the rock just before it hits the ground (approximate your answer)? m/s

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Impulse and momentum are related

as impulse applied to an object is equal to the change in momentum of the object

True

False

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How does the momentum of a bullet as it leaves the barrel of a gun compare to the recoil momentum of the gun?

The two momenta are equal (but opposite in direction)

The two momenta are not equal and not opposite in direction

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A moving object collides with a stationary one

Suppose a moving object collides with a stationary one and the two stick together. How will the speed of the stuck-together objects compare to the speed of the original moving object?

It will be more

It will be less

It will be equal

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Is momentum a scalar or a vector quantity?

Scalar

Vector

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Two blocks of ice are sitting on a table with a piece of dynamite between them

One block of ice has a mass of 12 Kg and the other's mass is 18 kg. The dynamite explodes. If the block of lesser mass moves off with a speed of 10 m/s, what is the speed of the more massive block?

m/s

Please type in the answer as it is wither it has a negative sign or not

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A 2000-pound car moving at 50 miles per hour collides with a stationary car weighing 3000 pounds

If the two cars stick together, what is their speed immediately after the collision?

Hint: On both sides of the equation, you may use "pounds" for mass and "miles per hour" for velocity. This is permissible because weight (pounds) is proportional to mass, and miles/hour is a legitimate unit of velocity.)

miles/hour

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Is the law of conservation of momentum violated if a gun is attached so firmly to a support that it cannot recoil?

Yes

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Work is the product of the force exerted and the distance through which it is exerted

True

False

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Holding a piano at shoulder

How much work is done in holding a piano at shoulder height for 15 minutes if the piano weighs 1200 newtons and your shoulder is 1.5 meters above the ground?

1800 joule

450 joule

27000 joule

No work is done

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Power is work done multiplied by the time used in doing the work

True

False

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As an object falls toward the ground, what happens to its potential energy?

It increases

It decreases

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Suppose two objects have the same mass, but one is moving twice as fast as the other

The kinetic energy of the fast one is how many times as great as the kinetic energy of the slow one?

two times

three times

four times

five times

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What happens to the kinetic energy of an object as the object falls?

It increases

It decreases

Nothing happens to it

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How does a perfectly elastic collision differ from an inelastic collision?

In (1) transparent , kinetic energy is conserved, but in (2) , it is not.

drag and drop the selected option to the right place

a perfectly elastic collision

an inelastic collision

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Lifting a 5-kg object 3 meters requires how much energy?

joules

approximate your answer without decimal points

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what is the power of the lifter if it requires 147 joules to lift an object above the ground for 2 seconds?

watts

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An object is going 10 m/s when it hits the ground.

From how high did it fall?

meters

Hint: Since the object's mass does not matter, you may choose any mass you want. and do not forget to approximate to the nearest first decimal point.

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