1- A weight lifter lifts a 390-N set of weights from ground level to a position
ID: 1547724 • Letter: 1
Question
1- A weight lifter lifts a 390-N set of weights from ground level to a position over his head, a vertical distance of 1.65 m. How much work does the weight lifter do, assuming he moves the weights at constant speed?
2-In 1990 Walter Arfeuille of Belgium lifted a 281.5-kg object through a distance of 17.1 cm using only his teeth. What magnitude force did he exert on the object during the lift, assuming the force was constant?
6- A mechanic pushes a 3.10 103-kg car from rest to a speed of v, doing 5,220 J of work in the process. During this time, the car moves 28.0 m. Neglecting friction between car and road, find v and the horizontal force exerted on the car.
(a) the speed v
m/s
(b) the horizontal force exerted on the car (Enter the magnitude.)
N
9- A daredevil on a motorcycle leaves the end of a ramp with a speed of 34.3 m/s as in the figure below. If his speed is 32.4 m/s when he reaches the peak of the path, what is the maximum height that he reaches? Ignore friction and air resistance.
11- A skier of mass 71 kg is pulled up a slope by a motor-driven cable.
(a) How much work is required to pull him 75 m up a 30° slope (assumed frictionless) at a constant speed of 2.3 m/s?
kJ
(b) What power (expressed in hp) must a motor have to perform this task?
hp
Explanation / Answer
1) F = 390 N , d = 1.65 m
W = F.d = 390*1.65
W = 643.5 J
2) m = 281.5 kg, d = 17.1 cm
F = mg
F = 281.5*9.8 = 2758.7 N
6) W = 5220 J, u = 0
from conservation of energy
W = 0.5mv^2 -0.5mu^2
5220 = 0.5*3.1*10^-3*v^2
v = 1835 m/s
(b) d = 28 m
W = F.d
5220 = F*28
F = 186 N
9) v = 34.3 m/s, u = 32.4 m/s
from kinematic equaitons
v^2 - u^2 = 2gh
34.3^2- 32.4^2 = 2*9.8*h
h = 6.47 m
11) m = 71 kg, d = 75 m
W = mgdsin(theta)
W = 71*9.8*75sin(30)
W = 26092 J
(b) P = F.v
P = mgsin(theta).v
P = 71*9.8*2.3sin(30)
P = 800 W
P = 1.07 hp
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