Railway Science (Physics-Work, Energy and Power)

Total Questions: 50

21. A set-up of having a large number of wind turbines working at a generate electrical energy on a large scale is called a - [RRB JE 29/05/2019 (Morning)]

Correct Answer: (d) Wind energy farm
Solution:

It is a clean and renewable energy source. Wind turbines harness energy from the wind using mechanical power to spin a generator and create electricity. Other renewable energy (Green energy) sources: Solar energy, Geothermal energy, Hydropower, Ocean energy, and Bioenergy.

22. In hydroelectric power plants, which energy is tapped using water turbines to drive generators? [RRB JE 27/06/2019 (Evening)]

Correct Answer: (a) Energy of falling water
Solution:

Energy of falling water rotates blades of a turbine, which then spins a generator that converts the mechanical energy of the spinning turbine into electrical energy. Solar power is energy from the sun that is converted into thermal or electrical energy.

23. A body rolling down on a hill has : [RRB Group D 17/09/2018 (Evening)]

Correct Answer: (d) Both kinetic energy and potential energy
Solution:

Kinetic Energy (KE) is the energy an object has because of its motion. Formula (KE) = 1/2 mv² , where m = mass and v = velocity. Example - A river flowing at a certain speed exhibits kinetic energy as the water possesses both velocity and mass. Potential Energy (PE) - An object can store energy due to its position. Formula (PE) = m g h, Where m = mass , g = gravitational force, h = height from the ground. Example - Tree branches high up the tree have potential energy because they can fall to the ground.

24. After a shell explodes, many fragments fly in different directions. What is preserved in this situation? [RRB Group D 17/09/2018 (Evening)]

Correct Answer: (a) momentum
Solution:

In the explosion, the initial kinetic energy is not conserved since initial energy is converted into different forms of energies. But momentum will be conserved since mass is divided into pieces with velocities in inverse proportion of mass.

25. _______ is the rate of doing work. [RRB Group D 17/09/2018 (Evening)]

Correct Answer: (c) Power
Solution:

Power = Work / time. SI unit - Watt (W) or joules per second (J/s).

26. The angle between displacement and force applied when no work is done is _________ [RRB Group D 17/09/2018 (Evening)]

Correct Answer: (d) 90°
Solution:

Work done = Force × Displacement × Cosθ. When θ = 90° then cos 90° = 0. Then work done is equal to zero. Other conditions : (i) when θ = 0°, work done is positive, (ii) when θ = 180°, work done is negative.

27. An object is released from a certain height above the ground. Just at the time it touches the ground, it will possesses ________ . [RRB Group D 18/09/2018 (Afternoon)]

Correct Answer: (a) Kinetic energy
Solution:

Kinetic energy is the energy of an object due to the virtue of its motion. When the body falls from height, the potential energy decreases but kinetic energy increases but overall energy remains constant. While, the energy an object possesses due to the virtue of its position is called its potential energy.

28. During the free fall of an object, which of the following energies increases at any point in its path ? [RRB Group D 19/09/2018 (Afternoon)]

Correct Answer: (c) Kinetic energy
Solution:

Kinetic energy is a form of energy possessed by an object due to its motion. Formula KE =  1/2 mv²  (‘KE’ is kinetic energy of the object, ‘m’ is mass of the object, ‘v’ is velocity). It depends on the mass of the object and its velocity. It must always be either zero or a positive value. Units (SI) - Joule (J). Examples - A river flowing at a certain speed exhibits kinetic energy as the water possesses both velocity and mass.

29. The kinetic energy of the particles is maximum in the case of _________. [RRB Group D 19/09/2018 (Afternoon)]

Correct Answer: (b) plasma
Solution:

Plasma possesses the most kinetic energy of the fundamental states of matter. This is because the particles in a plasma move faster than the other particles. The order of kinetic energy: Solids < Liquids < Gases < Plasma.

30. A car is moving with a high speed. Which energy does it possess? [RRB Group D 19/09/2018 (Afternoon)]

Correct Answer: (c) Kinetic energy
Solution:

Kinetic energy is a form of energy possessed by an object due to its motion. It is used by any moving object such as a person walking, a baseball being thrown, a crumb falling from a table. Formula, KE = 1/2 mv² , where m is
the mass of the body and v is the velocity of the body. It can never be negative and is a scalar quantity (It only provides the magnitude and not the direction).