AP Physics Unit 3 Review - Work, Energy, and Power

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15 Terms

1
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<p>Which block has more kinetic energy?</p>

Which block has more kinetic energy?

K1 = 1/2mv2 = K

K2 = 1/2m2v2 = 4K

Block 2 has 4 times the kinetic energy than block 1

2
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A 62kg person rides a 12kg bike and increases their speed from 3m/s to 4m/s my pedaling faster. What is the change in Kinetic Energy?

259 Joules

1/2*m*(Δv)2

1/2(74)(4)2 - 1/2(74)(3)2 = 259

3
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<p>Which Force provides the most work on the block? </p>

Which Force provides the most work on the block?

F1

4
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<p>Compare the three forces by amount of work done.</p>

Compare the three forces by amount of work done.

F3 < F2 < F1 - Forces above 90o have positive work, Forces equal to 90o have no work, forces above 90o have negative work.

5
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<p>Compare the magnitude of work done by each of the forces. (<span>θ<sub>1</sub>=θ<sub>3</sub>)</span></p>

Compare the magnitude of work done by each of the forces. (θ1=θ3)

F2 < F3 = F1

6
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<p>A pendulum swings upon an axis. There is a 2kg Mass connected to a string of negligible mass. The highest point is 5m higher then the bottom-most point. Which force provides the most work (F<sub>g</sub> or F<sub>t</sub>)?</p>

A pendulum swings upon an axis. There is a 2kg Mass connected to a string of negligible mass. The highest point is 5m higher then the bottom-most point. Which force provides the most work (Fg or Ft)?

Gravity

7
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<p>A pendulum swings upon an axis. There is a 2kg Mass connected to a string of negligible mass. The highest point is 5m higher then the bottom-most point. How much work is done by the force of tension.</p>

A pendulum swings upon an axis. There is a 2kg Mass connected to a string of negligible mass. The highest point is 5m higher then the bottom-most point. How much work is done by the force of tension.

0J - Forces perpendicular to displacement provide no work.

8
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<p>What information can you get from the graph?</p>

What information can you get from the graph?

Work done over n miles (area under the graph)

9
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What causes work?

  • A) Internal and External Forces

  • B) External Forces Only

  • C) External Forces and distance

  • D) Distance only

C) Distance and External Forces

10
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A cart initially at rest on a straight track speeds up with a constant acceleration until it reaches a speed of 20 m/s. Is there more work required to speed up frmo 0m/s to 10m/s, more for 10m/s to 20m/s or is it the same for both.

More from 10m/s to 20m/s

0m/s-10m/s = 1/2m(102) - 1/2m(02) = 1/2m100 = 50m J

10m/s - 20m/s = 1/2m(202) - 1/2m(102) = 1/2m300 = 150 J

Graph shows more displacement from 10-20; more displacement means more work (W=Fd)

<p>More from 10m/s to 20m/s</p><p>0m/s-10m/s = 1/2m(10<sup>2</sup>) - 1/2m(0<sup>2</sup>) = 1/2m100 = 50m J</p><p>10m/s - 20m/s = 1/2m(20<sup>2</sup>) - 1/2m(10<sup>2</sup>) = 1/2m300 = 150 J </p><p>Graph shows more displacement from 10-20; more displacement means more work (W=Fd)</p>
11
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<p>Two identical object move along a vertical track with the speeds on the graph. Which object experiences the most work?</p>

Two identical object move along a vertical track with the speeds on the graph. Which object experiences the most work?

Object 2 - Has a greater change in velocity

12
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<p>Compare the energy of the spring at each point.</p>

Compare the energy of the spring at each point.

1 < 2 < 3

1) Us (Equilibrium) = 0

2) Us = 1/2kx2

3) Us = 1/2k2x2 = 4 times more energy than point 2

13
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What factor does not affect Ug and Us?

  • A) Mass of object

  • B) Horizontal Displacement

  • C) Vertical Height

  • D) Speed

D) - Speed

Us = 1/2mkx2

Ug = mgh

14
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<p>A constant force F is exerted on a block that’s initially at rest. The block slides with negligible friction for equal distances d<sub>1</sub> and d<sub>2</sub>. <strong>Which of the quantities are equal for the two intervals.</strong></p><ul><li><p>A) Work done</p></li><li><p>B) Velocity</p></li><li><p>C) Kinetic Energy</p></li><li><p>D) Power</p></li></ul><p></p>

A constant force F is exerted on a block that’s initially at rest. The block slides with negligible friction for equal distances d1 and d2. Which of the quantities are equal for the two intervals.

  • A) Work done

  • B) Velocity

  • C) Kinetic Energy

  • D) Power

A) Work Done - Constance Force and same distance (W=Fd)

  • B) Object is acceleration

  • C) Work means change in energy

  • D) Non Constance velocity means non-constant change in power (P = Fv)

15
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<p>A horizontal force is applied to a 3kg box that is initially at rest. As the box speeds up, the force on the box decreases until their hand looses contact with the box. Friction is negligible.<strong> What is the speed of the box as the person’s hand looses contact with the box?</strong></p>

A horizontal force is applied to a 3kg box that is initially at rest. As the box speeds up, the force on the box decreases until their hand looses contact with the box. Friction is negligible. What is the speed of the box as the person’s hand looses contact with the box?

2.3 m/s

Calculate work by using the area of the graph, then set the work equal to kinetic energy.

5 = ½ 3m * v2