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

Total Questions: 16

11. Two balls of steel having mass of 5 kg and 10 kg each possess equal kinetic energy. Which ball is moving faster, if at all ? [RRB ALP Tier - I (29/08/2018) Afternoon]

Correct Answer: (d) The 5 kg ball is moving faster.
Solution:

12. If a boy covers a distance of 20 metre in 4 minutes with a force of 600 N, then the power consumed by the boy is: [RRB ALP Tier - I (29/08/2018) Evening]

Correct Answer: (d) 25 W
Solution:

Distance (d) = 20 m , Time (t) = 4 min ⇒
4 × 60 , [1 minute = 60 second] ⇒ 240 s ,
Force (F) = 600 Newtons.
Work (W) = Force (F) × distance(d) .
W = 600 × 20
⇒ 12000 N - m (Newton - Meter)
Power (P) = 𝑊𝑜𝑟𝑘 (𝑊)/ 𝑇𝑖𝑚𝑒 (𝑡) ⇒ 12000/240
P = 50 Watts.

13. A boy raises a box with a weight of 120 N through a height of 2 m. The work done by him is: [RRB ALP Tier - I (30/08/2018) Morning]

Correct Answer: (c) 240 J
Solution:

Given, F = 120 N, height or displacement (d) = 2 m, and Angle between force and displacement (cosθ) = 0°.
Since, Work done (W) = Force × displacement × cosθ.
So, W = 120 × 2 × cos 0° ⇒ 240 joule.

14. 9800 joule of energy was spent to raise a mass of 80 kg. The mass was raised to a height of. [RRB ALP Tier - I (30/08/2018) Afternoon]

Correct Answer: (a) 12.5 m
Solution:

Given, Energy (E) = 9800 Joules, Mass of the object (m) = 80kg, height = h Since the work is done against gravity, energy is stored in the object in the form of Potential Energy.
We know that potential energy (E)
= m × g × h
⇒ h = 𝐸/𝑚 ×𝑔  where gravity (g) = 9.8 m/s²
Now by substituting the above values in the above equation, we get
⇒ h = 9800/80 × 9.8 = 12.5 m (Approx)
Hence, The mass was raised to a height of h = 12.5 m.

15. A certain household has consumed 320 units of energy during a month. How much energy is this in joules? [RRB ALP Tier - I (30/08/2018) Evening]

Correct Answer: (c) 1152 × 10⁶ J
Solution:

1 unit of energy is equal to 1 kilowatt
hour (kWh).
1 unit = 1 kWh
1kWh = 3.6 × 10⁶J
Therefore, 320 units of energy
= 320 × 3.6 × 106 = 1152 × 10⁶ J.

16. If the momentum of a body is tripled, its KE will: [RRB ALP Tier - I (31/08/2018) Afternoon]

Correct Answer: (a) become nine times its original value
Solution: