To rescue a civilian from a destroyed subway tunnel, Captain America lowers a ro

Question

To rescue a civilian from a destroyed subway tunnel, Captain America lowers a rope into the tunnel and proceeds to use the wheel of an overturned automobile as a crude pulley. This allows Captain America to pull the rope parallel to the ground while lifting the civilian straight up. If it takes 2.75 seconds for Captain America to lift the 53.6 kg civilian a height of 1.80 m, taking her from rest to an upward velocity of 1.31 m/s in the process, what must be Cap's average power output? What must Cap's average power output be if he continues pulling her upward at 1.31 m/s?

Explanation / Answer

1. the power equals to the work done divided by the time duration

the work

w= mgh +1/2 mv^2 = 53.6 *9.8*1.80 +1/2*53.6*1.31^2

= 945.5 + 46.0

=991.5 J

P = 991.5/2.75 = 360.5 W

2. after reaching 1.31 m/s the power

P = mg*V = 53.6*9.8*1.31 = 688.1 W

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