MEDIUM
Earn 100

Assertion: When a spring is elongated work done by spring is negative but when it compressed work done by spring is positive.

Reason: Work done by spring is path independent.

50% studentsanswered this correctly

Important Questions on Work and Energy

EASY
Two equal masses are attached to two each of a spring of spring constant k. The masses are pulled out symmetrically to stretch the spring by a length x over is natural length. The work done by the spring on each mass is
MEDIUM

The graphs below show the magnitude of the force on a particle as it moves along the positive X-axis from the origin to X=X1. The force is parallel to the X-axis and conservative. The maximum magnitude F1 has the same value for all graphs. Rank the situations according to the change in the potential energy associated with the force, least (or most negative) to greatest (or most positive).

Question Image

EASY

The figure shows the variation of potential energy with distance. The part of the graph which represents the repulsive force is

Question Image

MEDIUM

In the figure, mass of A is m and that of B is 2m. All the surface are smooth. System is released from rest with spring unstretched. Then, the maximum extension Xm in spring will be

Question Image 

EASY
A block of mass 100 g moving at a speed of 2 m s-1 compresses a spring through a distance 2 cm before its speed is halved. Find the spring constant of the spring
MEDIUM

Two springs of force constants k1 and k2 are stretched by the same force. The ratio of potential energies stored in them is

EASY
A particle of mass m moves in a circular orbit under the central potential field, Ur=-Cr, where C is a positive constant. The correct radius - velocity graph of the particle's motion is :
EASY
Which one of the following is not a conservative force?
EASY
If a spring of spring constant 200 N m-1 is compressed by 5 cm, then the energy stored in the spring is
MEDIUM
The potential energy function for a two dimensional force is given by U=3x3y-7x. The force that acts at the point x, y is (Take i^ and j^ as unit vectors along X- and Y- axes)
EASY
Potential energy as a function of r is given by U=Ar10-Br5, where r is the interatomic distance, A and B are positive constants. The equilibrium distance between the two atoms will be :
HARD
A particle is moving in a circle of radius r under the action of a force F=αr2 which is directed towards centre of the circle. Total mechanical energy (kinetic energy + potential energy) of the particle is (take potential energy=0 for r=0):
MEDIUM
A 0.5 kg block moving at a speed of 12 m s-1 compresses a spring through a distance 30 cm when its speed is halved. The spring constant of the spring will be _____ N m-1.
HARD

Given below is the plot of a potential energy function U(x) for a system, in which a particle is in one dimensional motion, while a conservative force F(x) acts on it. Suppose that Emech =8 J, the incorrect statement for this system is :

Question Image

EASY
The potential energy of a system increases if work is done
MEDIUM
When a rubber-band is stretched by a distance x, it exerts a restoring force of magnitude
F = ax + bx2 where a and b are constants. The work done in stretching the unstretched rubber-band by L is :
MEDIUM
A block of mass m is kept on a platform which starts from rest with a constant acceleration g2 upwards, as shown in the figure. Work done by normal reaction on block in time t is,

Question Image
MEDIUM
A particle is released from a height H. At a certain height its kinetic energy is half of its potential energy with reference to the surface of the earth. Height and speed of the particle at that instant are respectively
MEDIUM
A uniform chain of mass  M and length L is lying on a smooth horizontal table, with half of its length hanging down. The work done in pulling the entire chain up the table is
MEDIUM
A particle with total mechanical energy which is small and negative is under the influence of a one dimensional potential Ux=x44-x22 J, where x is in meters. At time t=0 s, it is at x=-0.5 m. Then at a later time it can be found,