You are helping your friend prepare for her next skate board exhibition. For her

Question

You are helping your friend prepare for her next skate board exhibition. For her program, she plans to take a running start and then jump onto her heavy-duty 15-lb stationary skateboard. She and the skateboard will glide in a straight line along a short, level section of track, then up a sloped concrete wall. She wants to reach a height of at least 10 feet above where she started before she turns to comeback down the slope. She has measured her maximum running speed to safely jump on the skateboard at 7 feet/second. She knows you have taken physics, so she wants you to determine if she can carry out her programs as planned. She tells you that she weight 100 lbs and that her skateboard wheels are practically frictionless.

Explanation / Answer

The mass of skate boat, m1 = 15 lb = 6.8 kg The running speed, v = 7 feet/sec = 2.134 m/s The mass of her, m2 = 100 lb = 45.36 kg From the law of conservation of energy The potnetial energy = The kinetic energy          mgh = 0.5mv^2 The required height, h = 0.5v^2/g = 0.5*2.134*2.134 / 9.8                              h = 0.23 m So she will go the height to equal the kinetic enegy with potential energy is 0.23 m

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