Table of Contents
WORK POWER AND ENERGY JEE ADVANCED QUESTIONS
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11. The negative change of work done by conservative internal forces on a system is equal to the change in
(a) Total energy
(b) Kinetic energy
(c) Potential energy
(d) None of these
Ans. (c)
12. A large slab of mass 5 kg lies on a smooth horizontal surface, with a block of mass 4kg lying on top of it as shown in figure. The coefficient of friction between the block and the slab is 0.25. If the block is pulled horizontally by a force F=6N. The work done by the frictional force on the slab between instants t=2s to t=3s is (g = 10 m/s)
(a) 2.4 J
(b) 5.55 J
(c) 4.44 J
(d) 10 J
Ans. (b)
13. Two ends A and B of a smooth chain of mass m and length I are situated at a distance l/3 as shown in Fig. If an external agent pulls A until it comes to the same level as B, work done by the external agent is
14. The kinetic energy of a particle continuously increases with time.
(a) The resultant force on the particle must be parallel to the velocity at all instants.
(b) The resultant force on the particle must be at an angle less than 90
degrees all times.(c) Its height above ground level must be continuously decrease.
(d) The magnitude of its linear momentum is decreasing continuously.
Ans. (b)
15. A collar ‘B’ of mass 2 kg is constrained to move along a horizontal smooth and fixed circular track of radius 5 m as shown in Fig. The spring lying in the plane of the circular track and having spring constant 200 N/m is unperformed when the collar is at ‘A: If the collar starts from rest ‘B’, the normal reaction exerted by the track on the collar when it passes through ‘A’ is
(a) 360 N
(b) 720 N
(c) 1440 N
(d) 2880 N
Ans. (c)
Ans.(c)
Ans.(c)
18. A particle A of mass 10/7 kg is moving in the positive direction of x as shown in Fig. Its initial position is x = 0 and initial velocity at x=10 is (use the graph given)
(a) 80 J
(b) -80 J
(c) -180 J
(d) 180 J
Ans.(d)
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22. Which quantity of a two particle system depends only on the separation between the two particles?
(a) Kinetic energy
(b) Total mechanical energy
(c) Potential energy
(d) Total energy
Ans. (c)
23. A block is placed on a plank which is placed on a horizontal plane shown in Fig. A massless but elastic string deviates by an angle with vertical when a force F is applied to the plank to shift
it to the right making the block side over it. If Fp and FB are frictional forces between plank and plane and between block and plane, respectively then work done by applied force is given by
(a) Work done against friction acting on the plank + energy in the elastic string + work done by friction acting on block
(b) Work done against frictions acting on the plank and theblock + elastic energy
(c) Elastic energy of the string
(d) Difference of work done against frictions acting on the plank and the block
Ans. (a)
24. A moving railway compartment has a spring of constant k fixed to its front wall shown in Fig. A boy stretches this spring by distance x and in the mean time the compartment moves by a distances s. The work done by boy with respect to Earth is
27. The diagram in Fig. shows a plot of the potential energy as a function of displacement of a particle moving along the x axis:
Which of the following statement(s) is/are true?
(a) A, care points of
(b) A is a point of stable equilibrium
(c) B is not an equilibrium point
(d) all of the above
Ans. (d)
28. A 20 kg block attached to a spring of spring constant 5 N/m is released from rest at A. The spring at this instant is having an elongation of 1 m. The block is allowed to move in horizontal slot with the help of a constant force of 50 N in the rope as shown in Fig. The velocity of the block as it reaches B is (assume the rope to be light)
(a) 4 m/s
(b) 2 m/s
(c) 1 m/s
(d) 3 m/s
Ans. (b)
29. One end of a light spring of spring constant k is fixed to a wall and the other end is tied to a block placed on a smooth horizontal surface. In a displacement, the work done by the spring is (1/2) kx2. The possible cases are
(a) The spring was initially compressed by a distance 2x and was finally in its natural length
(b) It was initially stretched by a distance x and finally was in its natural length
(c) It was initially in its natural length and finally in a com pressed position
(d) It was initially in its natural length and finally in a stretched position
Ans. (b)
30. When a person stands on a weighing balance, working on the principle of Hooke’s law, it shows a reading of 60 kg after a long time and the spring gets compressed by 2.5 cm. If the person jumps on the balance from a height of 10 cm, the instantaneous reading of the balance will be
(a) 60 kg
(b) 120 kg
(c) 180 kg
(d) 240 kg
Ans. (d)
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