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

Total Questions: 50

11. An object of mass 14 kg is moving with a velocity of 5 m𝑠⁻¹ . Find the kinetic energy contained in the object ? [RRB Group D 11/10/2018 (Afternoon)]

Correct Answer: (d) 175 J
Solution:

Given : Mass of an object (m)= 14 kg,
velocity (v) = 5 m𝑠⁻¹ , Kinetic energy (K.E.)  = ?
We know that, Kinetic energy (K.E.)
= 1/2 × m × (v)² = 1/2 × 14 × (5)²
⇒ KE = 175 J.

12. Mass of an object is m = 30 kg and velocity of the object is v = 5 m/s. Find the kinetic energy of the object. [RRB Group D 11/10/2018 (Evening)]

Correct Answer: (d) 375 J
Solution:

Given that, m = 30 kg, v = 5 m/s
Now, K.E = 1/2 mv² , where K.E = Kinetic Energy, m = mass of object and v = Velocity of object.
K.E = 1/2 × 30 × (5)² ⇒ K.E = 375 J.

13. How much energy is contained in a 12 kg object when it is at a distance of 5 meters from the ground? Has been given 9.8 ms⁻² [RRB Group D 12/10/2018 (Morning)]

Correct Answer: (d) 588 J
Solution:

Potential Energy (P.E.) = mass (m) × gravity (g) × height (h)
Given that : mass (m) = 12 kg, gravity (g) = 9.8 m/s², height (h) = 5 m
P.E. = 12 × 9.8 × 5 ⇒ P.E. = 588 J.

14. When an object of 15 kg is at a height of 5 m from the ground, then what is the energy contained in it? Given g = 9.8 ms⁻² [RRB Group D 15/10/2018 (Morning)]

Correct Answer: (d) 735 J
Solution:

Given : Mass of the object (m) = 15 kg,
Height (h) = 5 m
Potential energy (P.E) = m × g × h
P.E = 15 × 9.8 × 5 ⇒ P.E = 735 J.

15. When an 11 kg object is at a height of 6 m from the ground, then what is the energy contained in it? Given g = 9.8 ms⁻². [RRB Group D 15/10/2018 (Evening)]

Correct Answer: (b) 646.8 J
Solution:

Given that, Mass of Object (m) = 11 kg,
Height = 6 m, Acceleration due to gravity (g) = 9.8 ms⁻² .
We know that, Potential energy = m × g × h = 11× 9.8 × 6 = 646.8 J.

16. What is the energy contained in an object of 11 kg when it is at a height of 8 m above the ground ? (Given that g = 9.8 ms⁻²) [RRB Group D 16/10/2018 (Morning)]

Correct Answer: (d) 862.4 J
Solution:

Given : Mass of the object (m) = 11 kg,
Height above the ground (h) = 8 m,
Acceleration due to gravity (g) = 9.8 m/s²
Potential energy (P.E.) = mass (m) × gravity (g) × height (h) = 11 × 9.8 × 8 = 862.4 J.

17. An object of mass m is raised to a height of 4h from ground level. Find the potential energy of the object. [RRB Group D 16/10/2018 (Afternoon)]

Correct Answer: (a) 4 mgh
Solution:

Given : The mass of the object (in kg) = m, the height = h, g = 9.8 m/s² Potential Energy (P.E.) = m × g × 4h = 4mgh.

18. A boy weighing 50 kg climbs 45 stairs in 9 s. If the height of each ladder is 15 cm then find its strength. Given, g = 10 ms⁻² [RRB Group D 16/10/2018 (Afternoon)]

Correct Answer: (d) 375 W
Solution:

19. Find the energy possessed by an object of mass 10 kg when it is at a height of 7 m above the ground ? Given g = 9.8 m𝑠⁻² ? [RRB Group D 22/10/2018 (Morning)]

Correct Answer: (b) 686 J
Solution:

Given : Mass of object m = 10 kg, Height h = 7m, Acceleration due to gravity g = 9.8 m/s2 .
Potential Energy of object P.E = m × g × h = 10 × 9.8 × 7 = 98 × 7 = 686 J.

20. An object of mass 12 kg is at a certain height above the ground. If the potential energy of the object is 600J, find the height at which the object is with respect to the ground. Given g = 10 ms⁻² [RRB Group D 22/10/2018 (Morning)]

Correct Answer: (b) 5 m
Solution:

Given : Object of Mass= 12 kg, Potential energy (P.E.) = 600 J, Acceleration due to gravity (g) = 10 ms⁻², Height (h) = ?
∵ Potential energy (P.E.) = mgh
= 12 × 10 × h.
⇒ 600 = 12 × 10 × h ⇒ h = 5 m.