Can someone please provide an explanation? 2. The work energy theorem states tha

Question

Can someone please provide an explanation?

2. The work energy theorem states that the work done by all the forces acting on an object is equal to the change in its kinetic energy. Use the concepts of work and energy to answer the following. (Note. this question can also be answered using Newton's laws and calculating accelerations. NO MARKS will be awarded for answering the question this way). A 20.0 kg mass is pushed 12 m across the floor by a 150 N force. a. What would the final velocity of the mass be if there were no friction? b. If the final velocity is actually observed to be 9.00 ms^-1, how large must the frictional force be?

Explanation / Answer

a) work done = F*d = 150*12

so kinetic energy = work done = 1800J

but kinetic energy = 0.5m*v*v = 0.5*20*v*v = 1800

so v= 13.41m/s

b) if v= 9 then loss in energy = 1800-0.5*20*9*9 = 990J = frictional energy

so frictional force = frictional energy/distance = 990/12 = 82.5 N

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