# HW#4b Page 1 of 6 Problem 1. A 100 kg person stands on a scale.

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### Problem 1. A 100 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 5 m/s2, 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 5 m/s2, 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/s2, 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.

I’ll use m = 100 kg, for parts b-c: accelerates upwards, downwards at 5 m/s2

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2

st

net

2

2

2

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2

2

2

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2

s

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11 N 11

static

0

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115 N 19.6

kinetic

95.4

9.542

static - max

s

s

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2

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2

s

k

2

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2

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## ) (5 m)11.82 m/s

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sin cos

sin tan cos

mg

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1 1

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### ( )

net net 2

88.82 N 20.71 N=68.11 N 68.11 N

a=F = 6.611 m/s

10 kg F

m

= −

=

2

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## ( )

1 2 2

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### definitely larger than the kinetic friction force, so the object has to accelerate.

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