Midterm 2 Solution

# Midterm 2 Solution - Q1(1pt A block with an initial...

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Q1 (1pt) A block with an initial velocity 10m/s comes a stop on a frictional surface. Which of the following is true? 1) The total of the mechanical energy of the block and thermal energy on the surface is not conserved because the frictional force is an external one. 2) The mechanical energy is conserved because the frictional force is an internal force between the surface and the block. 3) The total heat generated before it stops depends on the magnitude of the frictional force. 4) The amount of the heat generated is equal to the initial kinetic energy the block has. Answer : 4) Q2 (2pt) In a lecture demo, you see that a ball released from 1.25m above the ground reaches the floor with speed v before it bounces back to a maximal height h . Assume that the ball loses 20% of it mechanical energy after hitting the floor. v and h should be 1) v = 5m/s and h = 0.75 m; 2) v = 2.5m/s and h = 0. 9 m; 3) v = 2.5m/s and h = 1.05m; 4) v =5m/s and h = 1m. Answer: 4)

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Midterm 2 Solution - Q1(1pt A block with an initial...

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