Consider the following figure. (a) What force in newtons should the woman in the

Question

Consider the following figure.

(a)

What force in newtons should the woman in the figure exert on the floor with each hand to do a push-up? Assume that she moves up at a constant speed.

N

(b)

The triceps muscle at the back of her upper arm has an effective lever arm of 1.80 cm, and she exerts force on the floor at a horizontal distance of 21.2 cm from the elbow joint. Calculate the magnitude of the force in newtons in each triceps muscle.

N

Compare the magnitude of the total force exerted by both triceps muscles to her weight.

=

(c)

How much work does she do in joules if her center of mass rises 0.265 m?

J

(d)

What is her useful power output in watts if she does 22 push-ups in one minute?

W

Explanation / Answer

Applying Law of conservation of torque at point Fp

Fp*0 -W*0.90+Freaction*1.50=0

Freaction*1.50= W*0.90

Freaction=( W*0.90)/1.50

Freaction=(mg*0.90)/1.50

Freaction=(50*9.8*0.90)/1.50

Freaction =294.0N

Force exert by each force = Freaction /2 = 294/2 = 147.0 N

b)

Applying Law of conservation of torque

147*0.0180=Ftrices*0.212

Ftrices= 12.48

Ftrices/W = 12.48/(50*9.8) = 0.0255

c)

Work=mgh = 50*9.8*0.265 = 129.85 J

d)

P=nWork/t = (22*129.85)/60 = 47.61 W

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