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

Total Questions: 50

31. The work done in moving a charge from one point to the other is 20 J. If the potential difference between the points is to 10 V, the charge is : [RRB Group D 25/10/2018 (Morning)]

Correct Answer: (b) 2.0 C
Solution:

Given that : Work done (W) = 20 J,
Potential difference (V) = 10 V.
Since Work done (W) = Charge (Q) × Potential Difference (V).
Charge (Q) = 𝑊𝑜𝑟𝑘 𝑑𝑜𝑛𝑒 (𝑊)/𝑃𝑜𝑡𝑒𝑛𝑡𝑖𝑎𝑙 𝐷𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 (𝑉)
= 20/10 = 2 C.

32. A force of 25N is acting on an object. The object is moved 5 m in the direction of the force. The work done by the force will be _______. [RRB Group D 26/10/2018 (Afternoon)]

Correct Answer: (c) 125 J
Solution:

Given that : Force is = 25 N,
Displacement = 5 m
Work done is given as,
Work done (W) = Force (F) × Displacement (d) = 25 N × 5 m = 125 J.

33. How much work is done in moving a charge of 4 C across two points having a potential difference of 12 V? [RRB Group D 29/10/2018 (Morning)]

Correct Answer: (a) 48 J
Solution:

Given : Moving charge (Q) = 4 C, Two points having a potential difference of = 12 V
Work done, W = Q × V = 4 × 12 = 48 J.

34. A boy, of mass 50 kg. runs up a staircase of 41 steps in 10 s. If the height of each step is 15 cm, find his power. Take g = 10 ms⁻² [RRB Group D 29/10/2018 (Evening)]

Correct Answer: (b) 307.5 W
Solution:

35. How much work is done in moving a charge of 5 C across two points having a potential difference of 13 V ? [RRB Group D 29/10/2018 (Evening)]

Correct Answer: (b) 65 J
Solution:Given that : Charge (Q) = 5 C, Potential difference (V) = 13V, Work= ?
∴ Work = V × Q = 13 × 5 J = 65 J.

36. Find the energy possessed by an object of mass 10 kg when it is at a height of 6 m above the ground. Given g = 9.8 ms⁻² [RRB Group D 31/10/2018 (Afternoon)]

Correct Answer: (b) 588 J
Solution:

Given, Mass of object (m) = 10 kg, Height (h) = 6 m,
Acceleration due to gravity (g) = 9.8m/s² .
Potential Energy of object (P.E) = m × g × h
⇒ mgh = 10 × 9.8 × 6 = 98 × 6 = 588 J.

37. What is the amount of work done when a body moves under a force of 10N at a distance of 10 m in the direction of the force? [RRB Group D 31/10/2018 (Afternoon)]

Correct Answer: (a) 100 J
Solution:

Given : F =10 N, d = 10 m
∵ W = Force × displacement
W = F × d
W = 10 N × 10 m ⇒ W = 100 J.

38. A 10-kg object falls a distance of 4.0 m. The work done by the force of gravity acting on it is (take g = 10 m/s²): [RRB Group D 1/11/2018 (Evening)]

Correct Answer: (c) 400 J
Solution:

Given that : Mass of object (m) = 10 kg,
Acceleration due to gravity (g)= 10 m/s²,
Distance (s) = 4 m.
∵ Force = mass × acceleration
Work done = Force × Displacement = mass × acceleration × displacement = (mg) × displacement
Work done = (10 × 10) × 4 = 400 J.

39. An object of a certain mass is raised to a height of 5 m above the ground and its potential energy is 2000 J. What is the mass of the object? (take g = 10 ms⁻²) [RRB Group D 26/11/2018 (Afternoon)]

Correct Answer: (c) 40 kg
Solution:Given that : Potential energy (P.E.) = 2000 J, Height (h)= 5 m,
Acceleration due to gravity (g)= 10 ms⁻² .
∵ Potential energy (PE) = mgh
⇒ 2000 J = m × 10 × 5 ⇒ m = 40 kg.

40. An object of mass 3 m is raised to a height h above ground level. Find the potential energy of the object. [RRB Group D 27/11/2018 (Morning)]

Correct Answer: (c) 3 mgh
Solution:

Potential energy is the stored energy of position possessed by an object. Potential Energy (P.E.) = mass of the object (m) × g (gravitational field) × height of the object (h).
Given mass = 3 m, then P.E. of the object = 3m × g × h = 3 mgh.