A weightlifter works out at the gym each day. Part of her routine is to lie on h

Question

A weightlifter works out at the gym each day. Part of her routine is to lie on her back and lift a 43kgbarbell straight up from chest height to full arm extension, a distance of 0.54m .

Part A: How much work does the weightlifter do to lift the barbell one time?

Express your answer using two significant figures.

230

Part B: If the weightlifter does 22 repetitions a day, what total energy does she expend on lifting, assuming a typical efficiency for energy use by the body (25%).

E = 2.0

230

Explanation / Answer

Part A:

Mass m=43

Work done =force xdisplacement=mgxd=43x9.81x0.54=227.78J

Part B:

work done for 22 times lifting =227.78x22=5011.16J

for energy use by the body (25%).=5011.16/0.25=2.0x104J

1cal=4.18J

420cal=1755.6J

number of donuts =2x104/420x4.18=11.39donuts

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