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Chapter 9: Q 34PE (page 319)

Question: A father lifts his child as shown inFigure. What force should the upper leg muscle exert to lift the child at a constant speed?

Short Answer

Expert verified

The total force exerted by the upper leg muscle is 2254N.

Step by step solution

01

Define the force

A force is an external factor that can change the rest or motion of a body. It has a size and a general direction.

02

Free-body diagram

The diagram for the leg muscles is shown below:

03

Calculation of the force on the upper leg muscle

The net torque about the pivot point which is knee, is zero in equilibrium. We can write

FQ脳2=wleg脳20+wchild脳38

Here, the weight of the child is,

wchild=10脳9.8=98N

The weight of the leg is,

FQ脳2=39.2脳20+98脳38FQ=39.2脳20+98脳382FQ=2254N

Hence, the force is 2254N.

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