Railway Science (Physics-Work, Energy and Power) (Part-II)

Total Questions: 50

21. A body is falling from a height of 200 m. After it has fallen 100 m, the body will possess: [RRB Group D 29/10/2018 (Morning)]

Correct Answer: (d) half potential energy and half kinetic energy.
Solution:

Kinetic energy : The energy possessed by the body due to the virtue of its motion. Formula - K.E = 1/2 mv² Here,  m - mass, v - velocity and K.E - kinetic energy. Potential energy : The energy possessed by a body due to the virtue of its position or configuration. Formula - P.E = mgh. Here, m - mass, g - gravitational field strength and h - height.

22. Identify the example of a conventional source of energy. [RRB Group D 29/10/2018 (Evening)]

Correct Answer: (a) Natural gas
Solution:

Natural Gas - an odorless, gaseous mixture of hydrocarbons, predominantly made up of methane (CH₄). Usage - for generating electricity and heat. Natural gas in compressed form is used as fuel for vehicles (known as CNG). Solar energy - created by nuclear fusion that takes place in the Sun. Wind energy - Obtained from the force of the wind and created using a wind turbine. Nuclear energy - form of energy released from the nucleus, the core of atoms. It is the fifth-largest source of electricity for India after coal, hydroelectricity, solar, wind and gas power.

23. A more powerful engine can do more work in less time, such as an airplane covering more distance in less time than a car, consequently, an airplane is more powerful than a car. This is an example of which of these ? [RRB Group D 29/10/2018 (Evening)]

Correct Answer: (d) Power
Solution:

This represents the rate at which work is done, measured in Watts (W) and also measured in Joule/sec . Formula = Work / time. Dimensional Formula = [ML²T ⁻³].

24. Which of the following examples are of potential energy? [RRB Group D 31/10/2018 (Afternoon)]

a. A brick lying on the roof of a house.
b. The spring of a watch when wound up.
c. The compressed spring.
d. Water stored up in elevated reservoir in water-supply system

Correct Answer: (c) a, b, c, d
Solution:

Potential energy: The energy possessed by a body due to its change in position or shape. Examples - Compression or expansion of Spring, Water in Dams. Kinetic energy is the energy possessed by an object due to its motion. Examples - Hydropower Plants, Moving Car, Flying Airplane. The sum of kinetic energy and potential energy of an object is its total mechanical energy.

25. In which of the following cases, no work is done ? [RRB Group D 2/11/2018 (Afternoon)]

Correct Answer: (b) A donkey is walking with a weight on its back.
Solution:

If the donkey is walking but the weight on its back remains stationary (not moving), then no work is done on the weight. This is because there is no displacement of the weight in the direction of the force applied by the donkey. W = F.d cos(90) = 0.

26. Water flowing at a hydroelectric power station can rotate a turbine because it contains : [RRB Group D 2/11/2018 (Afternoon)]

Correct Answer: (c) kinetic energy
Solution:

More examples of kinetic energy: A baseball after it is thrown, An aeroplane has huge kinetic energy in flight, When an asteroid falls at an incredible speed, A car traveling down the road , and Ocean Waves.

27. What type of energy transformation occurs during thunder? [RRB Group D 12/11/2018 (Evening)]

Correct Answer: (b) Kinetic energy is converted into light and sound energy.
Solution:

Some other examples of energy transformations - Chemical Energy to Thermal and Light Energy: When we light a match stick, the chemical energy stored in the matchstick is converted into thermal and light energy. Solar Energy to Electrical Energy - In a solar photovoltaic (PV) system, solar energy from sunlight is converted into electrical energy by solar panels through the photovoltaic effect.

28. In solar energy collectors, maximum efficiency is achieved in __________: [RRB Group D 27/11/2018 (Evening)]

Correct Answer: (c) Paraboloid dish collector
Solution:

Parabolic dish collectors use a reflective dish in the shape of a paraboloid to focus sunlight onto a receiver located at the focal point of the dish. This concentration of sunlight results in very high temperatures at the receiver.

29. Which one of the following has only magnitude and no direction? [RRB Group D 4/12/2018 (Morning)]

Correct Answer: (c) Work
Solution:

Scalar Quantity - The physical quantities which have only magnitude and no direction. Example - Pressure, Energy, Frequency, Speed, Mass. Vector Quantity - The physical quantities which have both magnitude and direction. Example - Displacement, Force, Torque, Momentum, Acceleration, Velocity.

30. The work done by friction force is __________. [RRB Group D 4/12/2018 (Evening)]

Correct Answer: (c) always negative
Solution:

The force of friction always opposes the applied force. Friction opposes the relative motion between two surfaces in contact. It acts on both the surfaces. Friction depends on the nature of surfaces in contact.