Calculate the force a mother must exert to hold her 12.0 kg child in an elevator

Question

Calculate the force a mother must exert to hold her 12.0kg child in an elevator under the following conditions.

I just need to know how to do the ratio of this force.

A) The elevator accelerates upward at 0.850 m/s2.

- calculate the force in newton

- calculate the ratio of this force to the weight of the child
1

2  (b) The elevator moves upward at a constant speed.
-calculate the force in newton

- calculate the ratio of this force to the weight of the child
4

(c) The upward bound elevator decelerates at 2.30 m/s2.
-calculate the force in newton

- calculate the ratio of this force to the weight of the child

Explanation / Answer

Part A)

F = ma + mg

F = (12)(.85 + 9.8) = 127.8 N

ratio = 127.8/(12)(9.8) = 1.09

Part B)

F = mg = (12)(9.8) = 117.6 N

ratio = 117.6/117.6 = 1

Part C)

F = m(a-g)

F = (12)(-2.3 + 9.8) = 90 N

ratio = 90/117.6 = .765

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