# ps4b10 - Physics 111.01 September 24, 2008 PS 4b (10)...

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Physics 111.01 September 24, 2008 PS 4b (10) Problem 1. A 35 kg person stands on a scale. a.) What would be the scale readout? (How does this compare with the person's weight?) b.) If the person stands on the scale in an elevator accelerating upwards at 7 m/s 2 , what is the scale readout? (How does this compare with the person's weight?) c.) If the person stands on the scale in an elevator accelerating downwards at 7 m/s 2 , what is the scale readout? (How does this compare with the person's weight?) d.) If the person stands on the scale in an elevator accelerating downwards at 9.8 m/s 2 , what is the scale readout? (How does this compare with the person's weight?) e.) Explain why your result from part d makes sense. Is the actual weight of the person any different? What does the person perceive his weight to be? f.) If the person stands on the scale in an elevator moving up at a constant speed of 100 m/s, what is the scale readout? (How does this compare with the person's weight?) Explain why during most of the time during an elevator ride, a person will perceive nothing unusual. Solutions. (a) The person's weight is mass times g : W = (35 kg)(9.8 m/s 2 ) = 343 N. This is exactly the person's weight, though we usually measure our bulk in mass, in kg, rather than in force. (I am not sure where you find a scale that reads out in newtons.) (b) The scale is actually measuring the normal force on the person, and we now

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## This note was uploaded on 05/13/2010 for the course PHYSICS 111 taught by Professor Staff during the Fall '08 term at S.F. State.

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ps4b10 - Physics 111.01 September 24, 2008 PS 4b (10)...

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