Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev

DC Pandey (Questions & Solutions) of Physics: NEET

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NEET : Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev

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Introductory Exercise 6.1

Ques 1: A block is pulled a distance x along a rough horizontal table by a horizontal string. If the tension in the string is T, the weight of the block is W, the normal reaction is N and frictional force is F. Write down expressions for the work done by each of these forces.
Ans:
7x, O, O, - Fx
Sol: Work done by Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Work done by Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Work done by Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Work done by Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev

Ques 2: A particle is pulled a distance l up a rough plane inclined at an angle α to the horizontal by a string inclined at an angle β to the plane (α + β < 90°). If the tension in the string is T, the normal reaction between the particle and the plane is N, the frictional force is F and the weight of the particle is W. Write down expressions for the work done by each of these forces.
Ans:
 Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Sol: Work done by Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Work done by Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Work done by Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
= - Wl sin α
Work done by Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev

Ques 3: A bucket tied to a string is lowered at a constant acceleration of g/4. If the mass of the bucket is m and is lowered by a distance l then find the work done by the string on the bucket.
Ans: 
Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Sol:
Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev

 Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Work done by string Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev

Ques 4: A 1.8 kg block is moved at constant speed over a surface for which coefficient of friction Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev It is pulled by a force F acting at 45° with horizontal as shown in figure. The block is displaced by 2 m. Find the work done on the block by (a) the force F (b) friction (c) gravity.
Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Ans: 
(a) 7.2 j (b)  - 7.2 J (c) zero
Sol: μN = F cos 45°              …(i)
Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Substituting value of N from Eq. (ii) in Eq. (i).
Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Work done by force Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Work done by friction Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Work done by gravity Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev

Ques 5: A small block of mass 1 kg is kept on a rough inclined wedge of inclination 45° fixed in an elevator. The elevator goes up with a uniform velocity v = 2 m/s and the block does not slide on the wedge. Find the work done by the force of friction on the block in 1 s. (g = 10 m/s2)
Ans:
10 J
Sol: F = mg sin 45°
Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Displacement of lift in 1s = 2 m
Work done  by force of friction Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev

Ques 6: Two equal masses are attached to the two ends of a spring of force constant k. The masses are pulled out symmetrically to stretch the spring by a length 2x0 over its natural length. Find the work done by the spring on each mass.
Ans:
 Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Sol: Total work-done by spring on both masses
Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
= PE of the spring when stretched by 2x0
Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
∴  Work done by spring on each mass
Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev

Ques 7: Force acting on a particle varies with displacement as shown in figure. Find the work done by this force on the particle from x = - 4 m t o x = + 4 m .
Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
Ans: 
30J
Sol: Work done = Area under the curve
Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
= A+ A2 + A3 + A4
Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev Work, Energy and Power (Part - 1) - Physics, Solution by DC Pandey NEET Notes | EduRev
= 30 Nm

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