Answer:
(A)Workdone –140.022J (B) ΔPE –140.022J (C)
PE2 = –140.022J
Explanation:
The workdone by the gravitational force is given by the product of the force if gravity acting on the mass and the vertical displacement of the mass.
The for is the weight of the body.
W = mg
The vertical displacement = h
Workdone = W ×h = mgh
m = 1.60kg
g = 9.8m/s²
h = ‐8.93m
Workdone = –1.60×9.8×8.93 = – 140.022J
(b) From the work and energy theorem, which states that, the change in potential energy is the total workdone in displacing it vertically over a distance h.
So the change in potential energy, ΔPE = Workdone = –140.022J
(C)
Taking the top of the cliff as PE1 and the ground as PE2
PE2 – PE1 = workdone
Given that PE1 = 0J
So substituting the values in the equation above.
PE2 – 0 = –140.022J.
PE2 = –140.022J
In the whole of this calculation we did not need to use the velocity given or calculate the height the snowball rises during the course of its motion as the workdone in rising that height against gravity will be cancelled out by the force of gravity during descending part of the motion of the snowball as the force of gravity will do an equal but opposite (negative) work on the snowball. So for this kind of problem only the start and end points of the motion are important for consideration as every other point is traveled twice vertically. First going up and second when coming back down.
