Conceptual Questions Based on Class 11 Physics Work Energy and Power

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Here we are providing conceptual questions for Class 11 Physics Work Energy and Power. Answers are also provided along with questions. So that students can read and understand the question. These questions are prepared by the subject experts. Students can read these conceptual questions based on Work Energy and Power for better topic clarity and therefore will be able to score better marks in their exam.

Conceptual Questions Based on Class 11 Physics Work Energy and Power

Conceptual questions based on Class 11 Physics Chapter 6 Work Energy and Power is given below. Go through each and every question to understand the topic clearly.

Q.1. A body is moving along a circular path. How much work is done by the centripetal force?

Solution. For a body moving along a circular path, the centripetal force acts along the radius while the displacement is tangential i.e., 0 = 90°, therefore W = F.S. cos 90° = 0.

Q.2. How much work is done by a coolie walking on a horizontal platform with a load on his head?

Solution. Zero. In order to balance the load on his head, the coolie applies a force on it in the upward direction equal to its weight. His displacement is along the horizontal direction. Thus, the angle between force and displacement is 90°. Therefore, work done, W = Fs cos θ=Fs cos 90°=0.

Q.3. The earth moving around the sun in a circular orbit is acted upon by a force and hence work must be done on the earth by the force. Do you agree by this statement?

Solution. The statement is wrong. The gravitational force is a conservative force. So, the work done by the gravitational force over every complete orbit of the earth is zero.

Q.4. Is it possible that a body be in accelerated motion under a force acting on the body, yet no work is being done by the force? Explain your answer giving a suitable example.

Solution. Yes, it is possible, when the force is perpendicular to the direction ot motion. The moon revolves round the earth under the centripetal force of attraction of the earth, but earth does no work on the moon.

Q.5. A porter moving vertically up the stairs with a suitcase on his head does work. Why?

Solution. The porter lifts the suitcase vertically to the upstairs. Force has to be applied on the suitcase against the force of gravitation. Hence the porter does work.

Q.6. A man rowing boat upstream is at rest with respect to the shore. Is he doing work?

Solution. The boat is at rest with respect to the shore, but it is moving upstream with respect to water. The man is doing work relative to the stream because he is applying force to produce relative motion between the boat and the stream. But he does no work relative to the shore as displacement relative to the shore is zero.

Q.7. Does the work done in raising a suitcase on to a platform depend upon how fast it is raised up?

Solution. No. The work done depends on the force of gravity and the height through which the suitcase is raised. It does not depend on the time rate with which the suitcase is raised.

Q.8. Can a body have momentum without energy?

Solution. No, if a body has momentum, it must be in motion and consequently possess kinetic energy.

Q.9. In a tug of war one team is slowly giving way to the other. What work is being done and by whom?

Solution. The work is done by the winning team and is equal to the product of resultant force applied by the two teams and displacement that the losing team suffers.

Q.10. Explain, throwing mud on a wall is an example of perfectly inelastic collision.

Solution. When mud is thrown on a wall, it sticks to the wall. The kinetic energy of the mud is reduced to zero and there is non-conservation of kinetic energy. Hence it is a case of perfectly inelastic collision.

Q.11. Mountain roads rarely go straight up but wind up gradually. Why?

Solution. If the roads go straight up, the angle of slope θ would be large. In that case frictional force (f = μ my cos θ) would be less and the vehicles may slip. Moreover, while going up a large slope, a greater power would be required (as it will take less time).

Q.12. Can a body have energy without momentum?

Solution. Yes, there is an internal energy in a body due to the thermal agitation of the particles of the body, while the vector sum of the momenta of the moving particles may be zero.

Q.13. Can the overall energy of a body be negative?

Solution. Yes. As E = K + U, when U is negative and has magnitude greater than that of K, E is negative. For example, the energy of an electron bound to the nucleus of an atom is negative.

Q.14. Two bodies moving towards each other collide and move away in opposite directions. There is some rise of temperature of the bodies in the process. Explain the reason for the rise of temperature and state what type of collision is it.

Solution. Involved collision of the process is inelastic because the bodies suffer loss of kinetic energy which appears in the form of heat energy raising the temperature of the bodies.

Q.15. Does the potential energy of a spring decrease or increase when it is compressed or stretched?

Solution. The potential of the spring increases because work is done on it when it is compressed or stretched.

Q.16. What happens to the potential energy when (a) two protons are brought close together (b) one proton and one electron are brought close together?

(a) The potential energy increases when two protons are brought closer because work has to be done against the force of repulsion between them.

(b) The potential energy decreases when a proton and an electron are brought closer because work is done by the force of attraction between them (origin of the force being the system itself).

Q.17. “Chemical, gravitational and nuclear energies are nothing but potential energies for different types of forces in nature.” Explain the statement clearly with examples.

Solution. A system has potential energy, when various objects are held at certain distance against some force, by virtue of their position or configuration. Chemical potential energy results from the chemical bonding of atoms, gravitational potential energy results when objects are held at some distance against gravitational force while nuclear energy arises from the nuclear force between the nucleons.

Q.18. In a thermal power station, coal is used for the generation of electricity. Mention how energy changes from one form to another before it is transformed into electrical energy?

Solution. The heat energy produced due to combustion of coal converts water into steam. The heat energy of steam is converted into mechanical energy when it turns blades of a turbine. The mechanical energy so obtained is converted into electrical energy by the generators.


Conceptual Questions Based on Class 11 Physics

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