# Practice_Test_3_Answers - Solutions to Practice Test 3 1...

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Solutions to Practice Test 3 1. Which of the following is NOT a definition of kinetic energy of a moving object? Kinetic energy is a measure of the work done to put an object in motion, or it is a measure of the work done on a moving object to bring it to rest. a. Kinetic energy is a measure of the force acting on the object 2. If the velocity of an object doubles, its kinetic energy will: Since kinetic energy is proportional to the square of the velocity, doubling the velocity will result in the kinetic energy increasing four times. c. become four times its initial value 3. Which of the following statements about kinetic energy is NOT true? b. Kinetic energy is a vector quantity 4. Which of the following does NOT represent the work done by a force? Work is done by the component of the force in the direction of motion. So it is not correct to say that work is force multiplied by displacement. Work is displacement multiplied by the component of force in the direction of displacement. c. The force multiplied by the displacement 5.

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F (N ) x (m) 2 4 6 8 2 4 6 6 N A B C D The graph shows the force (F) versus displacement (x). Which of the following is a measure of the work done? Work done is given by the area under the force against time graph. In this case it is the area of the trapezoid ABCD. Here the parallel sides AB = 2 N and CD = 6 N. The perpendicular distance between them is 8 m. The area of the trapezoid ABCD is given by: 2.0 N + 6.0 N 8.0 m = 32 J 2 ⎛⎞ ⎜⎟ ⎝⎠ d. 32 J 6. Which of the following is not a unit of work? a. J s 7. A force of 50 N is applied at an angle 30 o with the horizontal to a wooden crate to move it along a floor a distance of 10. The work done on the crate is: The component of the force in the direction of displacement = 50 N cos 30 o = 43.3 N. Work done = 43.3 N x 10 m = 433 J c. 433 J 8. A spring with a spring constant k = 250 N/m is compressed 15 cm. The work done is: Work done on the spring in stretching it by x m is given by: 2- 1 2 11 W = kx = ×250 Nm ×(0.15m) =2.8 J 22 b. 2.8 J 9. What is the potential energy of the spring in question 8? Work done on the spring is stored as its potential energy. U = W b. 2.8 J
10. 2 m 2 kg 30 o h O A B C The figure shows a 2.0 kg ball suspended from the end of a rope 2.0 m long. What is the gain in potential energy of the ball when the string makes an angle of 30 o with the vertical? The ball is moved from its initial position A to position B. The vertical height h through which it is lifted = 2.0 m – OC. In triangle OCB, o OC Cos30 = OB . OC = OB cos 30 o = 2 cos 30 o = 1.73 m Therefore, h = 2.0 m – 1.73 m = 0.268 m The gain in potential energy is: U = mgh = 2.0 kg × 9.8 ms -2 × 0.268 m = 5.25 J a. 5.25 J 11. If the ball is now released, what will be the kinetic energy of the ball at the bottom of the arc? The potential energy gained in raising the ball becomes kinetic energy at the bottom of the arc. K = U = 5.25 J a. 5.25 J 12. What is the speed of the ball at the bottom of the arc in question 11?

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## This note was uploaded on 05/01/2011 for the course PHY 2048 taught by Professor George during the Fall '10 term at Edison State College.

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Practice_Test_3_Answers - Solutions to Practice Test 3 1...

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