7A_Practice_Problems 2011

7A_Practice_Problems 2011 - I.1) A Physics 7A student...

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I.1) A Physics 7A student stands on a chair and throws a 20g stone straight up in the air. As she lets go of the stone her hand is 2m above the ground. The stone lands on a vertical spring attached to the ground, compressing it fully (10cm) and the stone comes to rest at ground level. The spring constant is 100 N/m = 100 J/m 2 . What was the original speed of the stone? You must apply the Energy Interaction Model to receive full credit. I.2) Your DL instructor throws a solid heat-pack (mass = 100g) straight up in the air and asks you to graph the PE, KE, and Etotal between the time it leaves his hand and when it reaches the top of its flight path, motionless, 5m above the point of release. Draw this graph accurately for this range of motion, setting y=0 at the top of the heat-pack’s flight path. I.3) Plot PEgrav versus height between y=0m and y=20m for a 0.5kg ball thrown straight up on Earth and, on the same graph, for a ball thrown straight up on Jupiter (g Jupiter = 2.5*g Earth ). For each planet calculate the gravitational force at two different heights and add arrows of appropriate proportional strength and direction to your plot. I.4) At noon, while the sun is high overhead, a pendulum is pulled back so that it is raised to a height of 1.2 m above its original height. The pendulum is then released and swings gently back and forth. a) The graph below shows one of the energies of the swinging pendulum plotted vs. the horizontal position of the pendulum’s shadow on the ground. The energy shown is the (circle one): PE g KE E tot b) Draw in and label the other two energies so that the completed graph shows labeled plots of PE g , KE and E tot vs. the position of the swinging pendulum’s shadow on the ground. c) Using energy systems, find an algebraic expression for the speed of the pendulum at the bottom of its
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7A_Practice_Problems 2011 - I.1) A Physics 7A student...

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