A boy holds a 40-N weight at arm\'s length for 10 s. His arm is 1.5 m above the
ID: 1415144 • Letter: A
Question
A boy holds a 40-N weight at arm's length for 10 s. His arm is 1.5 m above the ground. The work done by the force of the boy on the weight while he is holding it is: 0 6.1 J 40 J 60 J 90 J Camping equipment weighing 6000 N is pulled across a frozen lake by means of a horizontal rope. The coefficient of kinetic friction is 0.05. How much work is done by the campers in pulling the equipment 1000 m if its speed is increasing at the constant rate of 0.20 m/s^2? -1.2 Times 10^6 J 1.8 Times 10^5 J 3.0 Times 10^5 J 4.2 Times 10^5 J 1.2 Times 10^6 J The amount of work required to stop a moving object is equal to the: velocity of the object kinetic energy of the object mass of the object times its acceleration mass of the object times its velocity square of the velocity of the object A man pushes an 80-N crate a distance of 5.0 m upward along a frictionless slope that makes an angle of 30 degree with the horizontal. His force is parallel to the slope. If the speed ofExplanation / Answer
Q1.
work done=force*displacement*cos(theta)
where theta=angle between force and displacement
here dispacement=0
hence work done=0
hence option A is correct.
Q2. force applied by the campers-friction force=mass*acceleration
=>force applied-0.05*6000=(6000/9.8)*0.2=122.45 N
==>force applied=422.45 N
distance travelled=1000 m
then work done by the campers=force*distance=422.45*1000=4.2245*10^5 J
hence option D is correct.
Q3.amount of work required to stop a moving object is equal to its kinetic energy as per energy conserrvation,
work done=change in kinetic energy of object
as final kinetic energy is zero because the speed is 0,
work done=initial kinetic energy of the object
hence option B is correct.
Q4. force applied by the man=F, let
component of weight of the crate along the incline=80*sin(30)=40 N
applying force balance equation:
F-40=mass*acceleration
==>F-40=(80/9.8)*(-1.5)
==>F=27.755 N
then work done=force*distance=27.755*5=138.775 J
hence option C is closest and correct answer.
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