Work Energy & Power
1. A block is a displaced from (1m, 4m, 6m) to 2î + 3ĵ − 4k̂ metre under a constant force F = 6î − 2ĵ + k̂
Newton. Find the work done by this force. (Ans: -2 J )
2. A block of mass 2.5 kg is pushed to 2.2 m along a frictionless horizontal table by a constant force 16 N
directed, 45o above the horizontal. Determine the work done
(a) By the applied force. (Ans: 24.9 J )
(b) The normal force exerted by table. (Ans: 0 )
(c) The force of gravity. (Ans: 0 )
(d) Determine the total work done on the block. (Ans: 24.9 J )
3. 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 a W ,the normal reaction is N and friction force is f. Write down
expressions for the work done by each of these forces. (Ans: 0,0 & -Fx )
4. A bucket tied to a string is a lowered at a constant acceleration g/4. If mass of bucket is ‘m’ and it is
𝟑𝒎𝒈𝒍
lowered by a distance 𝑙, then find the work done by the string on the bucket. (Ans:− )
𝟒
5. A 1.8 kg. block is moved at constant speed over a surface for which coefficient of friction is 0.25. It is
pulled by a force F acting 45o 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. (Ans: 7.2 J , -7.2 J , 0 )
6. A block is constrained to move along x axis under a force F = −2x. Here F is in Newton and x in metre.
Find the work done by the by this force. When the block is displaced from x= 2 m to x= - 4 m.
(Ans: -12 J )
4
7. A block is constrained to move along x axis under a force F = (x ≠ 0) .Here. F is in Newton x in metre.
x2
Find the work done by this force when the block is displaced from x = 4 m to, x =2 m. (Ans: -1 J )
8. 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 to x = 4 m. (Ans: 30 J )
9. By using graph find the work done by the force on a body as it moves
(a) From x = 10 m to x = 5 m. (Ans: -15 J )
(b) From x = 5 m to x = 10 m. (Ans: 15 J )
(c) From x = 10 m to x = 15 m. (Ans: 3 J )
(d) What is the total work done by the force over the distance,
From x = 0 m to x = 15 m. (Ans: 27 J )
10. By using rough calculate work done by the force.
(a) From x = 0 m to x = 3 m. (Ans: +4 J )
(b) From x = 3 m to x = 4 m. (Ans: 0 )
(c) From x = 4 m to x = 7 m. (Ans: -1 J )
(d) From x = 0 m to x = 7 m. (Ans: 3 J )
11. If the system is released from rest, find the work done by the string on both the blocks in one second.
𝟓𝟎 𝟏𝟎𝟎 𝟐𝟎𝟎 𝟐𝟎𝟎
(Ans: Wg1 = − J , Wg2 = − J , WT1 = J , WT2 = − 𝟗 J )
𝟑 𝟑 𝟗
12. A 10 kg block placed on a rough horizontal floor is being pulled by a constant force of 50 N. Coefficient of
kinetic friction between the block and the floor is 0.4. Find the work done by each individual force acting
on the block over a displacement of 5 m. (Ans: WF = 250 J ,Wg = 0 ,WN = 0 , Wf = - 200 J )
13. In Fig. (i), the man walks 2 m carrying a mass of 15 kg on his hand. In Fig. (ii), he walks the same distance
pulling the rope behind him. The rope goes over a pulley, and a mass of 15 kg hangs at its other end. In
which case is the work done by gravity is greater?
