(a)What force in newtons should the woman in the figure exert on the floor with

Question

(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 1.74 cm, and she exerts force on the floor at a horizontal distance of 21.6 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. total force exerted by both triceps muscles/ 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 20 push-ups in one minute? _______W

Explanation / Answer

1). Each hand experiences an equal reaction force Fr, so the condition for no net torque about the feet is:

0.900m×w =1.50m×2Ft

Ft = ((0.900m) (50.0kg) (9.80m/s2)) / 2(1.50m)

=147N downward

2). Ft×1.74cm =Fr×21.6cm

Ft =21.6cm / 1.74cm×147N

=1825N

2Ft / w=3650N / 440N

=8.3

=1825 N, 8.3 times her weight

3). W = Fd= mgd =(50.0kg)(9.80m/s2)(0.265m) =129.85J =130J

4). P = (W per pushup)(pushups per second)=(129.85J)(20pushups / 60s) =43.28W = 44W

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