Work, Energy and Power

This chapter has

Work, Energy and Power — solved practice questions

8 NEET Physics questions with step-by-step solutions. Attempt each, then reveal the answer.

1. Q1easy

   A force of 10 N moves a body through a displacement of 5 m, the angle between the force and displacement being 60 degrees. The work done by the force is:

   • A50 J
   • B25 J
   • C43.3 J
   • D12.5 J
   Show answer & solution

   Correct answer: (B) 25 J

   W = F d cos theta = 10 x 5 x cos 60 = 10 x 5 x 0.5 = 25 J.

2. Q2easy

   A body of mass 2 kg moves with a speed of 10 m/s. Its kinetic energy is:

   • A20 J
   • B50 J
   • C100 J
   • D200 J
   Show answer & solution

   Correct answer: (C) 100 J

   KE = (1/2) m v^2 = (1/2)(2)(10)^2 = 100 J.

3. Q3easy

   A spring of force constant 200 N/m is compressed by 0.1 m. The potential energy stored in the spring is:

   • A1 J
   • B2 J
   • C10 J
   • D20 J
   Show answer & solution

   Correct answer: (A) 1 J

   Elastic PE = (1/2) k x^2 = (1/2)(200)(0.1)^2 = (1/2)(200)(0.01) = 1 J.

4. Q4medium

   A pump lifts 100 kg of water per second to a height of 10 m. Taking g = 10 m/s^2, the minimum power of the pump is:

   • A1 kW
   • B100 kW
   • C5 kW
   • D10 kW
   Show answer & solution

   Correct answer: (D) 10 kW

   Power = (mgh)/t = (100 x 10 x 10)/1 = 10000 W = 10 kW (mass lifted per second is 100 kg).

5. Q5medium

   A particle of mass 5 kg has a linear momentum of 10 kg m/s. Its kinetic energy is:

   • A5 J
   • B10 J
   • C20 J
   • D50 J
   Show answer & solution

   Correct answer: (B) 10 J

   KE = p^2/(2m) = (10)^2/(2 x 5) = 100/10 = 10 J.

6. Q6medium

   If the momentum of a body is increased by 50%, its kinetic energy increases by:

   • A50%
   • B100%
   • C125%
   • D225%
   Show answer & solution

   Correct answer: (C) 125%

   Since KE is proportional to p^2, new KE ratio = (1.5)^2 = 2.25. So KE increases by 125%.

7. Q7medium

   A body of mass m is raised to a height h and then dropped. Just before hitting the ground its speed (neglecting air resistance) is:

   • Asqrt(2 g h)
   • Bsqrt(g h)
   • C2 g h
   • Dsqrt(g h / 2)
   Show answer & solution

   Correct answer: (A) sqrt(2 g h)

   By conservation of energy, mgh = (1/2) m v^2, so v = sqrt(2 g h). All potential energy converts to kinetic energy.

8. Q8hard

   A particle moves under a force F = 3x^2 (in newtons, with x in metres). The work done by this force in moving the particle from x = 0 to x = 2 m is:

   • A12 J
   • B24 J
   • C4 J
   • D8 J
   Show answer & solution

   Correct answer: (D) 8 J

   W = integral of F dx from 0 to 2 = integral of 3x^2 dx = [x^3] from 0 to 2 = 8 J.

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