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

Total Questions: 50

41. The work done in pulling up a block of wood weighing 2 kN for a length of 10 m on a smooth plane inclined at an angle of 15° with the horizontal is ________ [RRB Group D 05/12/2018 (Afternoon)]

Correct Answer: (a) 5.17 kJ
Solution:

42. If the speed of an object of mass 1 kg is _______, then its kinetic energy will be 1 joule. [RRB Group D 05/12/2018 (Evening)]

Correct Answer: (c) 1.4 m/s
Solution:

43. If a plane flies a distance of 4000 m with work done of 20000 J, then the force applied is : [RRB Group D 10/12/2018 (Morning)]

Correct Answer: (c) 5N
Solution:

Given : Distance (d) = 4000 m, Work (W) = 20000 J
Work (W) = Force (F) × displacement (d) ⇒ 20000 = F × 4000
⇒ F = 𝑊/𝑑 = 20000/4000 = 5 ⇒ F = 5 N.

44. A ball of mass m is moving with a momentum p. The Kinetic energy of the ball is: [RRB Group D 11/12/2018 (Morning)]

Correct Answer: (d)
Solution:

45. A wire suspended vertically from one of its ends is stretched by attaching a weight of 200 N to the lower end. The weight stretched the wire by 1 mm. Then the elastic energy stored in the wire is: [RRB Group D 11/12/2018 (Morning)]

Correct Answer: (a) 0.1 J
Solution:

Given : F = 200 N, x = 1 mm = 10⁻³ m
Elastic energy = 1/2 × F × x
= 1/2 × 200 × 1 × 10⁻³ = 0.1 J.

46. A man lifts a load of 20 kg to a height of 5 m from the ground. The work done by him is ___________. [g =10 ms⁻²] [RRB Group D 12/12/2018 (Afternoon)]

Correct Answer: (b) 1000 J
Solution:

Given : Mass (m) = 20 kg, h = 5 m, g = 10 m/s²
Work done (W) = mgh = 20 × 5 × 10 = 1000 J.

47. When a force of 10 N is applied, an object is displaced by 5 m. The work done will be ________. [RRB Group D 14/12/2018 (Morning)]

Correct Answer: (b) 50 J
Solution:

Given : Force on the object (F) = 10 N,
Displacement (d) = 5 m
Work done (W) = F x d = 10 x 5 = 50 J.

48. A body of mass 10 kg is moving with a constant velocity of 6 ms⁻¹ . What is the kinetic energy possessed by this body? [RRB Group D 14/12/2018 (Evening)]

Correct Answer: (b) 180 J
Solution:

Given : Mass of the body (m) = 10 kg, Velocity (v) = 6 ms⁻¹, Kinetic energy = ?
∵ Kinetic energy = 1/2 mv²
= 1/2 × 10 × (6)² = 180 J.

49. A 4.0 kg object is moving horizontally with a speed of 5.0 m/s. To increase its speed to 10 m/s, the amount of net work required to be done on this object is: [RRB ALP Tier - I (09/08/2018) Morning]

Correct Answer: (b) 150 J
Solution:

Net work required = 1/2 × 4 (10² - 5²) = 2(100-25) = 2 × 75 = 150 J

50. A body of mass 2 kg is thrown upward with initial velocity of 20 m / s. After 2 seconds, its kinetic energy will be: (g = 10 m/s²) [RRB ALP Tier - I (09/08/2018) Afternoon]

Correct Answer: (c) 0J
Solution:

Kinetic energy of an object is the measure of the work an object can do by the virtue of its motion. Newton’s first equation of motion, v = u + at, Where v = Final velocity , u = initial velocity, a = acceleration and t = time taken .
Body is moving upward, a = - g,
where g = acceleration due to gravity.
So, v = u – gt.
Given, u = 20 m/s , t = 2 sec and g = 10 m/s² .
We get, v = 20 – 10 × 2 = 0,
Kinetic Energy (K.E.) = 1/2 mv²
= 1/2 × 2 × 0² = 0