A weight lifter is bench-pressing a barbell whose weight is 710 N. He raises the barbell a distance of 0.65 m above his chest then he lowers it at 0.27 m. Determine the work done on the barbell by the weight lifter during:a.)the lifting phase and b.) the lowering phase.
To determine the work done on the barbell by the weightlifter during the lifting and lowering phases, we can use the formula:
Work = Force x Distance
a) The lifting phase:
Here, the weightlifter is applying a force to lift the barbell against gravity. Since there is no change in speed, we can assume that the force applied by the weightlifter is equal in magnitude and opposite in direction to the gravitational force acting on the barbell.
The formula for work during the lifting phase is:
Work = Force x Distance
The force applied during the lifting phase is equal to the weight of the barbell, which is 710 N. The distance raised by the barbell is 0.65 m.
Therefore, the work done on the barbell during the lifting phase is:
Work = 710 N x 0.65 m = 461.5 Joules
b) The lowering phase:
In the lowering phase, the weightlifter is now lowering the barbell back down. Again, assuming no change in speed, the force applied by the weightlifter is equal in magnitude and direction to the gravitational force acting on the barbell.
The formula for work during the lowering phase is the same:
Work = Force x Distance
The force applied during the lowering phase is still equal to the weight of the barbell, which is 710 N. The distance lowered by the barbell is 0.27 m.
Therefore, the work done on the barbell during the lowering phase is:
Work = 710 N x 0.27 m = 191.7 Joules
So, the work done on the barbell by the weightlifter during the lifting phase is 461.5 Joules, and during the lowering phase is 191.7 Joules.