A 35 kg crate is dragged upward along the side of a tall building by a rope that
ID: 2035600 • Letter: A
Question
A 35 kg crate is dragged upward along the side of a tall building by a rope that applies a 450 N force of tension. The crate scrapes against a vertical surface as it moves upward at constant speed 3.0 m/s. It is pulled upward a total distance pf 80.0 m.
a) How much work does the force of gravity do over the trip?
b) How much work does the force of tension do over the trip?
c) How much work does the normal force between the crate and the wall do over the trip?
d) What is the force of friction?
e) How much is power output required to move the crate upward via the rope's 450 N force of tension?
FT 450 N m-35 kgExplanation / Answer
a)
Work done by gravity Wg = m*g*y*cos180 = -35*9.8*80 = -27740 J
(b)
Work done by gravity WT = F*y*cos0 = 450*80 = 36000 J
(c)
work done by normal force WN = Fn*y*cos90 = 0
(d)
along vertical
speed is constant
acceleration ay = 0
net force Fy = m*ay = 0
net force = FT - Fg - f = 0
450 - 35*9.8 - f = 0
friction force f = 107 N
(e)
power = FT*v
v = speed = 3 m/s
Power P = 450*3 = 1350 W
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