Hi!
Work = change in Ec
= 1/2m(v1)² - 1/2m(v2)²
= 0 - 1/2 * 0,5 * 400
= - 100J
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Hola buddy . so umm what I can see from this is that to stop the ball the goalkeeper must do negative work against it . By applying work energy theorem which is ; work done = change in kinetic energy , we can get work done by the ball on hands of goalkeeper as -100 J ( keep initial velocity 20 m/s and final velocity as 0 m/s ) . so goalkeeper’s work on the ball would be 100J .
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Thank you very much!!!
Thank you so much!!!
One question the question, states work done on the ball, and work done is a scalar quantity. so why would it be -100 j why not 100. I understand that he is doing work in the opposite direction. But that doesn’t mean that work is vector. ( We know W = F X D. Work is the cross product of the two quantities).
If an object moves in the direction of the force acting on it, the work done by the force on the object is positive. In this process, the work done by forces acting in the opposite direction to the motion of the object is defined as negative work. Negative work can also be defined as an effect that reduces the mechanical energy of the body. So it doesn’t necessarily have to be a vector.