Railway Science (Physics-Force and Pressure) (Part-V)

Total Questions: 23

11. Two bodies of masses m and 9m are moving with equal kinetic energy. The ratio of their linear momentum will be. [RRB Group D 06/12/2018 (Afternoon)]

Correct Answer: (a) 1:3
Solution:

12. A block of mass 2 kg slides on a parallel surface with a speed of 4 m/s. It falls on an uncompressed spring and compresses it until the block becomes completely stationary. The amount of kinetic friction is 15 N and the spring constant is 10,000 N/m. The spring presses ______. [RRB Group D 10/12/2018 (Morning)]

Correct Answer: (b) 5.5 cm
Solution:

The kinetic energy of the spring is equal to its elastic potential energy, i.e. 1/2 mv² = 1/2 kx², when the spring is stretched some distance x from the equilibrium point and when its mass also has some velocity, v with which it is moving.
∵ 1/2 mv² = 1/2 kx²
⇒ 2  × 4² = 1000 × x²
⇒ x = 0.056 m = 5.5 cm.

13. The speed of a car increases from 36 km h⁻¹ to 54 kmh⁻¹ in 5 s. What will be the acceleration? [RRB Group D 11/12/2018 (Afternoon)]

Correct Answer: (a) 1 ms⁻²
Solution:

14. The mass of an object is 100 kg. What will be its weight on earth? (Given g = 9.8 ms⁻²) [RRB Group D 11/12/2018 (Evening)]

Correct Answer: (d) 980 N
Solution:

Given that : Mass of the object (m) = 100 kg,
Acceleration due to gravity (g) = 9.8 ms⁻²
Finding the weight of the object
∵ W = mg ⇒ W = 100 kg × 9.8 ms⁻² = 980 N.

15. The weight of an object on the Moon is ___________ times its weight on Earth. [RRB Group D 14/12/2018 (Morning)]

Correct Answer: (b) 1/6
Solution:

16. The weight of an object is 98 N. What will be its mass on earth? (Given g = 9.8ms⁻²) [RRB Group D 14/12/2018 (Afternoon)]

Correct Answer: (d) 10 kg
Solution:

Mass of the object (m) = 𝑊/g = 98 N/9.8 = 10 kg.

17. The weight of a boy on the surface of the moon is 300 N. The weight of the same boy on the surface of the earth will be: [RRB ALP Tier - I (13/08/2018) Afternoon]

Correct Answer: (a) 1800 N
Solution:

Since the acceleration due to the gravity of the moon is 1/6th of that of the earth. As a result, the weight of the boy on the surface of the earth will be 6 times higher than that on the moon. The weight of a boy on the surface of the moon is 300 N. The weight of the same boy on the surface of the earth will be 300 × 6 = 1800 N.

18. What will be the force of attraction between two bodies weighing 20 kg and 50 kg, respectively, with a distance of 2 metre between them? [RRB ALP Tier - I (17/08/2018) Morning]

Correct Answer: (d) 166.75 × 10⁻¹⁰ N
Solution:

19. A force of 20 N displaces an object through 2 m and does a work of 20 J. The angle between the force and displacement is: [RRB ALP Tier - I (20/08/2018) Afternoon]

Correct Answer: (a) 60°
Solution:

Work Done (W) is equal to the product of the force (F) and displacement (d). W = F × d × cosθ (θ is the angle between force and displacement)
Given: W = 20 J ; d = 2 m; F = 20 N
20 = (20 × 2) cos θ
1/2 = cos θ (for θ = 60°, we get cos value as 1/2)
So, the angle between the force and displacement is 60°.

20. What will be the acceleration produced when a force of 21 N is applied on an object of mass 3 kg? [RRB ALP Tier - I (21/08/2018) Morning]

Correct Answer: (b) 7ms⁻²
Solution:

Force: The interaction which after applying on a body changes or tries to change the state of motion or state of rest. S.I unit - Newton (N). Force (F) = Mass (m) × acceleration (a).
Acceleration = 𝐹𝑜𝑟𝑐𝑒/𝑀ass = 21/3 N-kg⁻¹ =  7ms⁻²