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

Total Questions: 50

41. Which of the following can neither be created nor be destroyed? [RRB ALP Tier - I (14/08/2018) Evening]

Correct Answer: (b) Energy
Solution:

Law of Conservation of Energy: Albert Einstein said that Energy cannot be created or destroyed. It can only be changed from one form to another. Force is that external cause which when acts on a body, changes or tries to change the initial state of the body. Momentum is the property of a moving body and is defined as the product of mass and velocity of the body. It is a vector quantity. The rate of doing work is called power. It is a scalar quantity.

42. What does the kinetic energy (KE) of a moving body depend upon? [RRB ALP Tier - I (14/08/2018) Evening]

Correct Answer: (b) Mass and velocity
Solution:

The energy possessed by an object due to its motion is called kinetic energy. K.E. = 1/2 mv², where m is the mass and v is the velocity of the object. The kinetic energy of a body or object depends upon its velocity and mass.

43. What is the type of Energy possessed by a stretched rubber band ? [RRB ALP Tier - I (14/08/2018) Evening]

Correct Answer: (c) Potential energy
Solution:

(Stored energy) - The energy possessed by a body due to its position. Potential energy (PE) = m g h. Example - stretched rubber band, A water tank on a rooftop. Example - A soaring baseball, a crumb falling from a table. Thermal energy is produced when the atoms and molecules in a substance vibrate faster due to a rise in temperature. Example - Boiling water on a stove, The heat from a heater.

44. If a body is whirled in a circle, then the work done on it ________ . [RRB ALP Tier - I (17/08/2018) Evening]

Correct Answer: (c) is zero
Solution:

When a body is whirled in a circle, then work done on it is zero because in circular motion displacement is always perpendicular to the applied force. The angle between the radius and the tangent is 90°.
Work done (W) = force × displacement × angle between them. W = F S cosθ. If cos 90° = 0 then work done = 0.

45. In which of the following activities is work NOT done? [RRB ALP Tier - I (20/08/2018) Morning]

Correct Answer: (c) Ashwin is standing on the platform
Solution:

The work done by a force acting on an object is equal to the magnitude of the force multiplied by the distance moved in the direction of the force. Work has only magnitude and no direction. Hence, work is a scalar quantity. The SI unit of work is Joule (J).

46. A compressed spring possesses more energy than a spring of normal length because the compressed spring has: [RRB ALP Tier - I (20/08/2018) Morning]

Correct Answer: (a) potential energy
Solution:

Potential energy is the energy stored by an object due to its relative position to other objects. P.E. = mgh, where m (mass in kilograms), g (acceleration due to gravity in m/s²) and h (height in meters). Examples - A water tank on the rooftop. Chemical energy - Energy produced by the breaking and forming bond between chemical atoms or molecules. Heat energy - Energy produced due to the motion of molecules.

47. Work done by a passenger standing on a platform holding a suitcase weighing 10 kg is: [RRB ALP Tier - I (21/08/2018) Morning]

Correct Answer: (a) 0 J
Solution:

Work done: Magnitude of the force multiplied by the distance moved by the object in the direction of the applied force. SI unit - Joule (1 Joule = 1 Newton × 1 meter) (Scalar quantity). Work done (W) = F × s cosθ, where F = force applied, s = displacement and θ = angle between force and displacement. Here, the Person is not covering any distance as he is just standing holding a suitcase. So displacement (s) = 0 Therefore, the work done by a person is ⇒ W = F.s cos θ = 0 Joule.

48. In a hydro-electric power station ultimately which energy is converted into electrical energy? [RRB ALP Tier - I (29/08/2018) Morning]

Correct Answer: (a) Kinetic energy
Solution:

Kinetic energy is the energy an object has because of its motion; Example - A Person walking, A thrown baseball, A crumb falling from a table, A charged particle in an electric field. Heat energy is the result of the movement of tiny particles called atoms, molecules or ions in solids, liquids and gasses. The SI unit for energy - Joule (J).

49. When a bullet is fired from a gun, its potential energy is converted into: [RRB ALP Tier - I (29/08/2018) Evening]

Correct Answer: (b) kinetic energy
Solution:

When a bullet is fired, the chemical energy in form of potential energy is converted into kinetic energy and heat thereby moving the bullet out of the barrel. Mechanical energy - the sum of potential and Kinetic energy. Kinetic energy: the energy an object has because of its motion. K.E. = 1/2 mv².
Example - A person walking, a soaring baseball, a crumb falling from a table.

50. While releasing the arrow from a stretched bow, the PE of the bow is converted into? [RRB ALP Tier - I (30/08/2018) Morning]

Correct Answer: (d) kinetic energy
Solution:

It is a form of energy which helps an object to remain in motion. K.E. = 1/2 mv² , where, m = mass and v = velocity, SI unit (Joule). Heat energy - Energy produced due to the motion of molecules. Example: Melting Ice and Baking in an oven.