Energy Problems (Sheet A)



Work & Kinetic Energy – Part 1

What is energy? In Physics, it is the ability to ________________.

What are the different types of energy?

____________________ ____________________ ____________________ ____________________

Let’s look at an object initially at rest that is acted on by a constant force for a time Δt during which it is displaced by Δd. During this displacement, it acquires a velocity of v2.

Since energy is the ability to do work, the work done on this object is known as its __________________,

or the energy to do _____________. Like work, energy is a ____________ that has units of ____________.

The work-energy theorem

Answers to reverse side:

1) 90,000 J; 250 J; .24 J 2) 3.2 m/s; 5.6 kg 3) 200 J; -200 J; -800 J

4) -32,000 j; 32,000 J 5) 1 J, 1 m/s; 4 J, 2 m/s; 8 J, 2.8 m/s; 8 J, 2.8 m/s; 7 J, 2.6 m/s

6) 2,250 J; 2,250 J; 22.5 m 7) 15 m/s [E]; -7500 J; -7500 J 8) 6000 J; -1500 J

Work/KE Problems: part 1

1. Calculate the kinetic energy of each of the following:

a) an 800 kg automobile moving at 15 m/s.

b) a 2.0 g rifle bullet moving at 500 m/s

c) a 0.50 kg ball accelerated from rest by a force of 8.0 N for 3.0 cm

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2. Two toys, one with a mass of 3.2 kg and the other with a velocity of 2.4 m/s, each have the same kinetic energy of 16 J. Determine the velocity of the first toy, and the mass of the 2nd.

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3. A baseball of mass 250 g, pitched with a speed of 40 m/s, is caught by a catcher, whose glove moves backward at 0.25 m while stopping the ball.

a) What is the kinetic energy of the ball.

b) How much work did the catcher’s glove do in stopping the ball?

c) What average stopping force was exerted on the ball?

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4. A bullet of mass 12 g strikes a stationary fixed block of wood at a speed of 400 m/s, penetrating to a depth of 3.0 cm. Calculate the average net force acting on the bullet while it’s in the wood. Then, calculate the average force exerted on the wood by the bullet.

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5. The graph shows the horizontal force on a 2.0 kg

trolley as it moves 5.0 m along a straight, level,

frictionless track, starting from rest. Determine

its kinetic energy and velocity after each meter that

it moves.

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6. A man pushes a 20 kg box from rest across the ground with a constant force of 100N. If the block acquires a final velocity of 15 m/s, find:

a) the kinetic energy of the block at the end.

b) the work done in pushing the block.

c) the distance that the block traveled.

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7. A 200 kg go-cart which was traveling 10 m/s westward is now traveling 5 m/s eastward. Find:

a) the total change in velocity, Δv, during the trip.

b) the total change in Kinetic Energy, ΔKE, during the trip.

c) the total work done on the go-cart during the trip.

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8. A 40 kg wagon is moving with constant horizontal velocity of 10 m/s.

a) How much work must be done to double this velocity?

b) How much work must be done to halve the original velocity?

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Kinetic Energy Potential Energy

Day #3

+ gain

W = ΔE

- loss

Mechanical Chemical Nuclear Electrical

do work

Joules (N-⥭഍䶓瑯潩鑮഍楋敮楴⁣湅牥祧഍捓污牡഍ግ䔠䉍䑅䔠畱瑡潩⹮″ᐠᔁ––䵅䕂⁄煅慵楴湯㌮†Ĕ䔕䉍䑅䔠畱瑡潩⹮″ᐠᔁ഍–䵅䕂⁄煅慵楴湯㌮†Ĕക഍഍഍഍m)

“Motion”

Kinetic Energy

Scalar

[pic][pic]EMBED Equation.3 [pic]

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In-Class work/KE problems (a little on the challenging side ()

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