A) 17.8 kg block is dragged over a rough, horizontal surface by a constant force
ID: 2040048 • Letter: A
Question
A) 17.8 kg block is dragged over a rough, horizontal surface by a constant force of 131 N acting at an angle of 29.8 ? above the horizontal. The block is displaced 39.9 m, and the coefficient of kinetic friction is 0.22. The acceleration of gravity is 9.8 m/s 2 .Find the work done by the force of friction. Answer in units of J.
B)A 6.4 kg bowling ball is lifted 1.6 m into a storage rack. The acceleration of gravity is 9.8 m/s 2 . Calculate the increase in the ball’s potential energy. Answer in units of J.
C)Mary weighs 505 N and she walks down a flight of stairs to a level 3.1 m below her starting point. What is the change in Mary’s potential energy? Answer in units of J.
Explanation / Answer
given
m = 17.8 kg
F = 131 N
theta = 29.8 degrees
d = 39.9 m
mue_k = 0.22
g = 9.8 m/s^2
A) Normal force acting on the block, N = m*g - F*sin(theta)
= 17.8*9.8 - 131*sin(29.8)
= 109.3 N
Workdone by friction, W_friction = fk*d*cos(180)
= mue_k*N*d*(-1)
= -0.22*109.3*39.9
= -959 J
b) increase in ball's potential energy = m*g*delta_h
= 6.4*9.8*1.6
= 100.4 J
c) change in potential energy = m*g*delta_h
= 505*(-3.1)
= -1566 J
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