EPChap08-Solution1 - Chap 8 HW1 Questions 2 In Figure 8-21...

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1 Chap. 8 HW1 Questions 2. In Figure 8-21, a horizontally moving block can take three frictionless routes, differing only in elevation, to reach the dashed finish line. Rank the routes according to (a) the speed of the block at the finish line In (1) gravity will do a negative amount of work on the block, so its KE and therefore its speed will decrease In (2) gravity will do zero work on the block, so its KE and therefore its speed will not change In (3) gravity will do a positive amount of work on the block, so its KE and therefore its speed will increase Ranking is: 3, 2, 1 (b) the travel time of the block to the finish line, greatest first. Travel time depends on velocity, fastest has the smallest travel time Ranking is 1, 2, 3 Problems 6. A 1.50 kg snowball is fired from a cliff 12.5 m high. The snowball's initial velocity is 14.0 m/s, directed 41.0° above the horizontal. (a) How much work is done on the snowball by the gravitational force during its flight to the flat ground below the cliff? (b) What is the change in the gravitational potential energy of the snowball–Earth system during the flight? (c) If that gravitational potential energy is taken to be zero at the height of the cliff, what is its value when the snowball reaches the ground? The force of gravity is constant, so () ( )( ) J 184 m 5 . 12 m/s 8 . 9 kg 5 . 1 . 2 = = = = mgh d F W v v (b) Δ U = – W = –184 J. (c) Δ U=U f U i . Since U i = 0 U = –184 J - 0 = -184 J
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2 7. In Figure 8-33, a small block of mass m = 0.032 kg can slide along the frictionless loop-the-loop, with loop radius R = 12 cm. The block is released from rest at point P , at height h = 5.0R above the bottom of the loop. How much work does the gravitational force do on the block as the block travels from point P to (a) point Q ?
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This note was uploaded on 04/07/2008 for the course PHYS 213 taught by Professor Oshea during the Spring '08 term at Kansas State University.

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EPChap08-Solution1 - Chap 8 HW1 Questions 2 In Figure 8-21...

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