No work is done when
1. a nail is plugged into a wooden board
2. a box is pushed along a horizontal floor
3. there is no component of force parallel to the direction of motion
4. there is no component of force normal to the direction of force
1 kW h is equal to
1. 3.6 J
2. 3.6 MJ
3. 3.6 kJ
4. 36 J
A body of mass 1 kg has a kinetic energy of 1 J when its speed is
1.
2.
3.
4.
The unit of work is joule. The other physical quantity that has same unit is
1. Power
2. Velocity
3. Energy
4. Force
An electic motor creats a tension of 4500 N in hoisting a cable and reel it at a rate of . The power of the motor is
1. 25 kW
2. 9 kW
3. 225 kW
4. 90 kW
The unit of work is joule. The other physical quantity that has same unit is
1. Power
2. Velocity
3. Energy
4. Force
In which of the following cases is work done maximum
1.
2.
3.
4.
The work done by a weight of 1 kg mass when it moves up through 1 m is
1. 10 J
2. -10 J
3. 0.1 J
4. -0.1 J
A man carries a suitcase in his hand climbs up the stairs. The work done by the man is
1. positive
2. negative
3. zero
4. none of the above
If Rahul has done the same amount of work in less time compared to Rohan then
1. Rahul has more power
2. Rohan has more power
3. both Rahul and Rohan have equal power
4. Rahul has more energy than Rohan
Which of the following is not an example of potential energy?
1. water stored in a dam
2. a stretched bow and arrow system
3. a dog chasing a hare
4. a stone lying on the top of a roof
Chlorophyll in plant converts light energy into
1. heat energy
2. chemical energy
3. mechanical energy
4. electric energy
A person pulls a body on a horizontal surface by applying a force of 5.0 N at an angle of with the horizontal. Find the work done by this force in displacing the body through 2.0 m.
1.
2.
3.
4.
In an electric flashlight the chemical energy of the cell is
1. converted into heat energy only
2. converted into light energy only
3. converted first into light and then heat energy
4. converted first into heat and then light energy
A student carries a bag weighing 5 kg from the ground floor to his class on the first floor that is 2 m high. The work done by the boy is
1. 1 J
2. 10 J
3. 100 J
4. 1000 J
When a force retards the motion of a body, the work done is
1. positive
2. zero
3. negative
4. undefined
A nail becomes hot when hammered in a plank
1. the potential energy of hammer changes into heat energy
2. the kinetic energy of the hammer changes into heat energy
3. the force of friction changes into heat energy
4. none of the above
What should be the angle between the force and displacement for maximum work?
1.
2.
3.
4.
Two bodies have their masses and their kinetic energies . The ratio of their velocities are
1. 1:1
2. 1:2
3. 1:3
4. 2:3
If force and displacement of the particle (in direction of force ) are doubled. Work should be
1. doubled
2. 4 items
3. halved
4. 1/4 times
Which of the following statements is correct regarding the relation between centripetal force and radius of the circular path?
1. The work done by th ecentripetal force increase if the radius of the path is increased
2. The work done by the centripetal force decreases by decreasing the radius
3. The work done by the centripetal force increases by decreasing the radius
4. The work done is always zero
A body rolls down on an inclined plane, it has
1. only kinetic energy
2. only potential energy
3. both kinetic energy and potential energy
4. neither kinetic energy nor potential energy
In which of the following case is the potential energy of a spring minimum?
1. When it is compressed
2. When it is extended
3. When it is at its natural length
4. When it is at its natural length but is kept at a height h above the ground
A uniform force of 4 N acts on a body of mass 8 kg for a distance of 2.0 m. The K.E acquired by the body is
1. 8 J
2. 64 J
3. 4 J
4. 16 J
A boy has four options to move a body through 3 m as indicated. In which case is maximum work done?
1. Push over an inclined plane
2. Lift vertically upwards
3. Push over smooth rollers
4. Push on a plane horizontal surface
The speed of a motor bike decreases by 4 times, its kinetic energy will decrease by
1. four times
2. eight times
3. sixteen times
4. thirty two times
Watt sec represents the unit of
1. energy
2. power
3. force
4. none of these
A rocket rises up in the air due to the force generated by the fuel. The work done by the
1. fuel is negative work and that of force of gravity is positive work
2. fuel is positive work and that of force of gravity is negative work
3. both fuel and force of gravity do positive work
4. both fuel and force of gravity do negative work
A ball is thrown upward from a point P, reaches to the highest point Q
1. kinetic energy at P is equal to kinetic energy at Q
2. potential energy at P is equal to kinetic energy at Q
3. kinetic energy at P is equal to potential energy at Q
4. potential energy at P is equal to potential energy at Q
A stretched spring possesses
1. kinetic energy
2. elastic potential
3. electrical energy
4. magnetic energy
Which one of the following is not the measure of energy?
1. kW h
2. erg
3. W s
4. J s
In a factory due to a sudden strike the work usually done in a day took a longer time. Then
1. power increases
2. power decreases
3. energy increases
4. energy decreases
When the momentum of a body is increased by 100%, its K.E increases by
1. 100%
2. 200%
3. 300%
4. 400%
A certain household consumes 250 units of electric energy in a month. The energy consumed in megajoule is
1. 900 MJ
2. 750 MJ
3. 2250 MJ
4. 1750 MJ
When the speed of a particle is doubled, the ratio of its kinetic energy to its momentum
1. remains the same
2. gets doubled
3. becomes half
4. becomes four times
An iron sphere of mass 30 kg has the same diameter as an aluminium sphere whose mass is 10.5 kg. the spheres are dropped simultaneously from a cliff. When they are 10 m from the ground, they have the same
1. acceleration
2. momentum
3. potential energy
4. kinetic energy
Two boys A and B lift 100 bricks through the same height in 5 minutes and 6 minutes respectively.
1. A has more power than B
2. B has more Power than B
3. both have same power
4. none of the above
A rocket rises up vertically. What happens to its potential energy?
1. it increases
2. it initially increases then decreases
3. it initially decreases then increases
4. it increases, till it becomes maximum
A locomotive exerts a force of 7500 N and pulls a train by 1.5 km. The work done by the locomotive in megajoule is
1. 12.25 Mj
2. 11.25 Mj
3. 10.75 MJ
4. 11.50 Mj
A car weighing 500 kg working against a resistance of 500 N, accelerates from rest to in 100 m. What is the work done by the engine?
1.
2.
3.
4. Data is insufficient
A man of weight 60 kg wt takes a body of mass 15 kg at a height 10 m on a building in 3 minutes. The efficiency of man is
1. 10%
2. 20%
3. 30%
4. 40%
Figure shows the frictional force versus displacement for a particle in motion. The loss of kinetic energy (work done against friction) in travelling over s = 0 to s = 20 m will be
1. 80 J
2. 160 J
3. 240 J
4. 24 J
A body falling from a height of 10 m rebounds from a hard floor. It loses 20% of energy in the impact. What is the height to which it would rise after the impact?
1. 7 m
2. 5 m
3. 8 m
4. 6 m
one koliwatt is approximately equal to
1. 1.30 h.p
2. 1.56 h.p
3. 2.50 h.p
4. 1.83 h.p
Which of the following graph best represents the total energy (T) of a freely falling body and its height (h) above the ground?
1.
2.
3.
4.
The momentum of a body is doubled. What is the percentage increase in kinetic energy?
1. 500%
2. 300%
3. 200%
4. 600%
If a body is raised through height h on the surface of earth and the energy spent is E, then for the same amount of energy the body on the surface of moon will rise through the height of
1. 2 h
2. 6 h
3. 4 h
4. 12 h
Which of the following graph best represents the kinetic energy (K.E) of a freely falling body and its height h above the gdround?
1.
2.
3.
4.
A stream engine has an efficiency of 20%. It is given an energy of 1000 cal. per minute. What is the actual work done by it in joule and in calories?
1. 100 cal, 800 J
2. 200 cal, 873 J
3. 10 cal, 80 J
4. 100 cal, 100 J
The mass of a ball A is twice the mass of another ball B. The ball A moves at half the speed of the ball B. The ratio of the kinetic energy of A to that of B is
1.
2.
3.
4.
A cricket ball is projected vertically upward such that it returns back to the thrower. The variation in kinetic energy with time is best represented by
1.
2.
3.
4.
When the momentum of a body is increased by 100%, its K.E increases by
1. 100%
2. 200%
3. 300%
4. 400%