A hill is 150 m long and makes an angle of 12° with the horizontal.As a 60-kg jogger runs up the hill,how much work does gravity do on the jogger?
A)8.82E+4 J
B)1.83E+4 J
C)−1.83E+4 J
D)8.63E+4 J
E)zero

Question

Quizplus · Accepted Answer

Gravity only acts vertically downwards, so it does no work on the jogger moving horizontally up the hill. The work done by gravity is given by the formula W = mgh, where m is the mass of the jogger, g is the acceleration due to gravity (9.81 m/s^2), and h is the height gained by the jogger. The height gained can be found by using trigonometry: 
h = 150 sin(12°) = 30.94 m
So the work done by gravity is W = (60 kg)(9.81 m/s^2)(30.94 m) = -1.83 x 10^4 J (negative because the work done by gravity is in the opposite direction to the displacement of the jogger). Therefore, the best answer choice is C.

A Hill Is 150 M Long and Makes an Angle