Two friends, Joe and Sam, go to the gym together to strength train. They decide

Question

Two friends, Joe and Sam, go to the gym together to strength train. They decide to start off with an exercise called flat bench press. Lying flat on a bench with their arms in an extended position, they slowly lower (to their chest) and then raise a barbell back to the starting position. They start off by using a 39.0 kg barbell. Joe is taller than Sam which means Joe's arms are 69.6 cm long while Sam's are 60.4 cm. Calculate the work done by Joe, WJoe, when he raises the barbell to finish one repetition. The acceleration due to gravity is 9.81 m/s2.

Remember Sam also does the exercise. How does the amount of work Sam does, WSam, lifting the weight compare to Joe? Choose the correct operator from the list below.

Explanation / Answer

work done is equal to= force *distance travelled *cos (angle between force and distance )

force required = mg =39*9.81=382.59 N

angle is 0 degree since force will be applied in the direction of movement of barbell

Distance by Joe in bringing the weight to chest point=69.6 cm =0 .696 m

work done by joe in bringing the weight to chest point =0.696*382.59=266.28 J

same work will be done to lift to same position =266.28 J

total work in one repitition =532.56 J

Distance by Sam in bringing weight to chest point=60.4 cm = 0.604 m

work done by Sam in bringing weight to chest point=382.59*0.604=231.08 J

same work will be done to bring to starting position = 231.08

total work in one repitition=462.16 J

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