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

Total Questions: 50

21. A car falls off the side of the road and hits the ground in 0.5 s. If g is equal to 10 ms⁻² , what is its speed when it hits the ground? [RRB Group D 03/10/2018 (Evening)]

Correct Answer: (d) 5 ms⁻¹
Solution:

Given that, Acceleration, a = g = 10 ms⁻² ,
Time of fall, t = 0.5 s
Let, initial velocity, u = 0
Now, Speed on striking the ground,
v = u + at = 0 + 10 × 0.5 = 5.0 ms⁻¹.

22. The mass of an object is 20 kg. What would its weight be on Earth ? (take g = 10 ms⁻²) [RRB Group D 03/10/2018 (Evening)]

Correct Answer: (d) 200 N
Solution:

Given, m = 20 kg.
W = m × g ⇒ W = 20 × 10 = 200 N.

23. The speed of a car increases uniformly from 18 kmh⁻¹ to 36 kmh⁻¹ in 5s. Calculate the acceleration of the car. [RRB Group D 04/10/2018 (Morning)]

Correct Answer: (b) 1 ms⁻²
Solution:

Given that, Initial velocity (u) = 18 km/hr = 5 m/s, Final velocity (v) = 36 km/hr = 10 m/s, Time (t) = 5 sec
Using the first equation of motion,
v = u+ at
⇒ 10 = 5 + a (5) ⇒ a = 1 m/sec².

24. A 20 g bullet with a velocity of 150 ms⁻¹ is fired horizontally from a 2.5 kg pistol. What is the recoil velocity of the pistol? [RRB Group D 04/10/2018 (Afternoon)]

Correct Answer: (a) -1.2 ms⁻¹
Solution:

25. The weight of an object on the earth is 200 N and mass is 20 kg. What is the value of acceleration due to gravity given? [RRB Group D 05/10/2018 (Morning)]

Correct Answer: (b) 10 m/s²
Solution:

Weight = mass х acceleration due to gravity,
Given , Weight = 200 N and Mass = 20 kg.
Then, Acceleration due to gravity = 200/10 = 10 m/s².

26. A bullet, of mass 20 g is horizontally fired with a velocity 150 ms⁻¹ from a pistol of mass 3 kg. What is the recoil velocity of the pistol? [RRB Group D 05/10/2018 (Morning)]

Correct Answer: (c) -1.0ms⁻¹
Solution:

The recoil velocity of the pistol can be calculated using the following equation : m₁(mass of the bullet) × v₁ (velocity of the bullet)= m₂ (mass of the pistol) × v₂(velocity of the pistol).
(0.020 kg) × (150 ms⁻¹) = (3 kg) × v₂ ⇒ v₂ = 1.0 ms⁻¹
Therefore, the recoil velocity of the pistol is - 1.0 ms⁻¹ (The recoil velocity is in the opposite direction of the velocity of the bullet).

27. The weight of an object on earth is 60 N. What would be its weight on the Moon ? [RRB Group D 05/10/2018 (Afternoon)]

Correct Answer: (a) 10 N
Solution:

Given that, the weight of the object on the earth surface (Wₑ)= 60 N.
We know that,
Weight of the object on the moon (Wₘ)
= 1/6 × Wₑ = 1/6 × 60 = 10 N.

28. A 25 g bullet is fired horizontally with a velocity of 150 ms⁻¹ from a pistol of 2 kg. What is the expected velocity of the pistol ? [RRB Group D 05/10/2018 (Afternoon)]

Correct Answer: (d) - 1.87 ms⁻¹
Solution:

Given : Mass of the bullet (m) = 25 grams = 0.025 kg, Velocity of bullet (v) = 150 m/s, Mass of the pistol (M)= 2 kg, Velocity of pistol (V) = ?
∵ Initial momentum of the system is ‘0’ as it is at rest.
After firing,
V= - 𝑚𝑣/m = - 0.025 × 150/ = 2 =  - 1.87 ms⁻¹.

29. A bullet, of mass 30 g is horizontally fired with a velocity 150 ms ⁻¹ from a pistol of mass 2 kg. What is the recoil velocity of the pistol? [RRB Group D 05/10/2018 (Evening)]

Correct Answer: (a) - 2.25 ms⁻¹
Solution:

30. The weight of an object on the earth is 200 N. What is its mass (g = 10 ms⁻²)? [RRB Group D 05/10/2018 (Evening)]

Correct Answer: (a) 20 kg
Solution:

Given : Weight of Object = 200 N,
Acceleration due to gravity = 10 m/s².
∵ Weight of the Object = Mass ×Acceleration due to gravity
Mass = 𝑊𝑒𝑖𝑔ℎt/𝐴𝑐𝑐𝑒𝑙𝑒𝑟𝑎𝑡𝑖𝑜𝑛 𝑑𝑢𝑒 𝑡𝑜 𝑔𝑟𝑎𝑣𝑖𝑡y = 200/10 = 20 kg.