## WORK ENERGY AND POWER Quiz-12

Work power energy is the most important chapter when it comes to mechanics, for JEE (Advanced). The chapter is quite tricky and takes a lot of time and devotion on your part to understand and master. But this chapter is a complete gold medal for almost all the questions of the mechanics can be solved by the work power energy approach if you master this topic..

Q1.
•
•
•
•
Solution

Q2.
A man places a chain (of mass m and lengthl) on a table slowly. Initially, the lower end of the chain just touches the table. The man brings down the chain by length l/2. Work done by the man in this process is
•  -mg l/2
•  -mgl/4
•  -3mgl/8
•  -mgl/8
Solution

Q3.
•  4 m/s
•  2 m/s
•  3√2 m/s
•  100/3 m/s
Solution

Q4.
A man M_1 of mass 80 kg runs up a staircase in 15 s. Another man M_2 also of mass 80 kg runs up the same staircase in 20 s. The ration of the powers developed by them will be
•  1
•  4/3
•  16/9
•  None of these
Solution
Power P=Work/Time
Work done by both will be same
Hence, P1/P2 =t2/t1 =20/15=4/3

Q5.
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•
•
•
Solution

Q6.
•  Only statement i is correct
•   Only statement ii is correct
• Only statement iii is correct
•  All the statements are correct
Solution

Q7.
•  mgl/36
•  mgl/15
•  mgl/9
•  None of the above
Solution

Q8.
A 40 kg box is pushed along 20 m by two coolies over a railway platform whose coefficient of friction with the box is 0.4. The forces applied by the two coolies are horizontal. If g=10 ms^(-2), then the work done by the two coolies is
•  +1600 J
•  -1600 J
•  +3200 J
•  -3200 J
Solution
Work done =Î¼ mg S=04×40×10×20 J=3200 J

Q9.
•  Same
•  Double
•  Triple
•  Half
Solution
Effective length becomes double during sudden release

Q10.
A small block of mass 2 kg is kept on a rough inclined surface of inclination Î¸=30° fixed in a lift. The lift goes up with a uniform speed of 1 ms^(-1) and the block does not slide relative to the inclined surface. The work done by the force of friction bon the block in a time interval of 2 s is

•  Zero
•  9.8 J
•  29.4 J
• 16.9 J
Solution

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