Work And Energy - MCQ Test (22-11-2017) - Class 9 MCQ

When a body moves on a circular path. The force that acts on the revolving body towards the center is called centripetal force. As the force acts as right angle to the direction of motion, so work done is 0.

In physics, a work is said to be done when there is some displacement on the body on which force is applied. Work done is +ve when the body is displaced in direction of applied force.

Potential Energy of a body = mgh, hence the potential energy is maximum when you are standing, given that acceleration due to gravity and mass remain constant.

According to the law of conservation of energy, energy neither be created nor be destroyed, it can be transformed from one form to another. So, all the statements are true.

Work done when a body moves at an angle to the direction of force is W = F cos ϕ ×s. The value of Cos is maximum for 0°. So, work done will be maximum for this angel.

One Giga watt is equal to 10⁹ watt or 10⁶ kilowatt. The rate of doing work is called as power. Hence both statements are correct.

An aeroplane flying at an altitude possesses both kinetic energy and potential energy. Kinetic energy is due to mass and velocity and potential energy is due to mass and height.

1 kwH =1000 W×60×60 s= 3600000J= 3.6 × 10⁶ J. one watt is equal to one joule per second.

Initial velocity (u)= 0, final velocity (v) =10 m/s, V²−u² 2= 2gh, 100–0 =2×10×h. h= 100/20 = 5m.

Power of lamp = 100w = 100/1000 = 0.1Kw, time= 5 hrs. Electrical energy = power×time, E =0.1kw×5h= 0.5 kw–h. = 0.5 unit.

The potential energy of a freely falling object decreases progressively due to decrease in height. Kinetic energy is converted into heat and sound energy when a freely falling object on reaching the ground. Work is done only when change in position occurs.

The total energy of the system is always conserved. It is just transformed from one form to other form. Mechanical energy of a system is not conserved. It is converted into other form of energy.

1 watt second (W.S) = 1J/s×s = 1 joule.

No work is done in reading a book, pulling wall of house and walking on a level road with book on his head as there is no change in the position of object on which force is applied. Stretching string causes displacement, so it is a work.

When you compress a coil spring you do work on it. The elastic potential energy increases.

The gravitational force of the earth on a satellite along a circular path is O as gravitational force of earth acts on right angle which is O for cos.

1 unit (Kw-H) = 3.6×10⁶ joule. Therefore, 250 units = 250×3.6×10⁶joule = 9×10⁸ Joule.

Correct Options:

• Newton metre


• Joule


• Kilowatt hours

Explanation:

The unit of energy is a measure of the ability of a system to do work or produce heat. The correct options for the unit of energy are:

• Newton metre: This is the unit of energy in the metric system. It is defined as the amount of energy transferred when a force of one newton is applied over a distance of one metre.


• Joule: This is the SI unit of energy. It is defined as the amount of energy transferred when a force of one newton is applied over a distance of one metre. It is the most commonly used unit of energy.


• Kilowatt hours: This is a unit of energy commonly used for measuring electricity consumption. It is equal to the energy consumed by a 1 kilowatt (kW) device operating for one hour.

Therefore, options A, B, and C are correct. The unit of energy can be measured in Newton metre, Joule, and Kilowatt hours.

Potential energy of a spring increases when it is in the state of expansion and compression. Elastic potential energy increases with compression and gravitational potential energy increases on expansion.

Momentum = mass x velocity, velocity = momentum/ mass = 16/2 = 8m/s. Kinetic energy = ½ mv2. K.E = ½ x2 x 82 = 64 J.

Electron volt is an unit of energy. One electron volt is equal to 1.6×10⁻¹⁹ joule. One mega electron = 1.6×10⁻¹⁹joule×100000=1.6×10⁻¹³joules.

The kinetic energy of a freely falling object which eventually stops on reaching the ground changes into heat and sound energy.

Displacement is the shortest distance between initial and final position of the body. Displacement may be due to acceleration due to gravity during free fall.

Potential energy = mgh, here, P.E = 9800 j. mass = 50kg, g = 9.8m/s². Therefore, 9800 = 50×9.8×h, h = 9800/50×9.8= 20m.

Kinetic energy of a body is K.E =1/2 mv². Kinetic energy depends upon mass of the body and velocity. Since mass and velocity never be negative, kinetic energy is always positive.

Momentum is the product of mass and velocity. P = 2×u, u = p/2. Again p = 4×v, v = p/4. So, velocity of first particle is twice the second. Ratio of kinetic energy =(1/2×2×p/2×p/2)/(1/2×4×p/4×p/4) = 2/1 = 2:1.

When a body is thrown vertically upwards, during its upward movement the potential energy is increase due to increase in height and kinetic energy decreases due to decrease in velocity.

One kg of butter provides more energy to human body after digestion in comparison to 1 kg of rice, potatoes and salad.

With increase in temperature, the kinetic energy of molecules increases and start vibrating with faster speed. Potential energy depends on height so, when a body falls towards the surface of the earth, its P.E decreases.