Challenging Physics Problems Based on Work, Energy, Power and Conservation Laws for JEE Advanced

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This series contains exhaustive collection of challenging problems of all the varieties being asked in JEE (Advanced) Examinations. Here, we have provided collection of the best possible problems for IIT-JEE (JEE Advanced) based on topic Work, Energy, Power and Conservation Laws.

Challenging Physics Problems Based on Work, Energy, Power and Conservation Laws for JEE Advanced with Answers

Q.1. A block of mass 1 kg is pulled along the curve path ACB by a tangential force as shown in figure. The work done by the frictional force when the block moves from A to B is

(a) 5 J
(b) 10 J
(c) 20 J
(d) none of these

Answer

Answer: (c)

Q.2. As shown in the figure, there is no friction between the horizontal surface and the lower block (M = 3 kg) but friction coefficient between both the blocks is 0.2. Both the blocks move together with initial speed v towards the spring, compresses it and due to the force exerted by the spring, moves in the reverse direction of the initial motion. What can be the maximum value of v (in cm/s) so that during the motion, there is no slipping between the blocks. (use g = 10m/s²)

(a) 20 cm/s
(b) 10 cm/s
(c) 30 cm/s
(d) 40 cm/s

Answer

Answer: (a)
Maximum chance of slipping occurs when spring is maximum compressed. At this moment, as force exerted by the spring is maximum, acceleration of the system is maximum. Hence maximum friction force is required at this moment.
By W/E theorem

Q.3. A massive disc of radius R is moved with a constant velocity u on a frictionless table. Another small disc collides with it elastically with a speed of v0 = 0.3 m/s, the velocities of the discs being parallel. The distance d shown in the figure is equal to R/2, friction between the discs is negligible. For which u (in m/s) will the small disc move perpendicularly to its original motion after the collision ?

(a) 0.1
(b) 0.5
(c) 1.0
(d) 0.01

Answer

Answer: (a)

Q.4. A ball of mass m collides horizontally with a stationary wedge on a rough horizontal surface, in the two orientations as shown. Neglect friction between ball and wedge. Two student comment on system of ball and wedge in these situations.

Aman : Momentum of system in x-direction will change by significant amount in both cases.
Ragini : There are no impulsive external forces in y-direction in both cases hence the total momentum of system in y-direction can be treated as conserved in both cases.
(a) Aman is wrong and Ragini is correct
(b) Aman is correct and Ragini is wrong
(c) Both are correct
(d) Both are wrong

Answer

Answer: (d)
In Case-I no horizontal external impulse on ball and mass system while in Case-II friction is impulsive as normal with ground is impulsive. Therefore, both are wrong.

Q.5. A body of mass 10 g is attached to a hanging spring whose force constant is 10 N/m. The body is lifted until the spring is in its unstretched state. The body is then released. Calculate the speed of the body when it strikes a table 15 cm below the release point.
(a) 0.831 m/s
(b) 0.512 m/s
(c) 1.121 m/s
(d) 2.142 m/s

Answer

Answer: (a)