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What will be work done on a body of mass 5 kg to increase its speed from 4 m/s to 8 m/s?
1. 60
2. 180
3. 240
4. 120

1 Answer

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Best answer
Correct Answer - Option 4 : 120

CONCEPT:

  • Kinetic Energy: When a body is in linear motion, it's energy due to motion will be kinetic energy.

Mathematically:

K = 1/2 × m × v2

where K is the kinetic energy of the body, and m is the mass of the body, and v is its velocity.

  • Work-Energy Theorem: The net work done on an object is equal to a change in its Kinetic energy.

W = ΔK

W = Kf -K

where W is work done, Kf is final kinetic energy and Ki is initial kinetic energy.

CALCULATION:

Given that initial velocity = 4 m/s

final velocity = 8 m/s

mass of body = 5 Kg

so initial kinetic energy K= 1/2 × m × v2 = 1/2 × 5 × 42 = 40 J

final kinetic energy Kf = 1/2 × m × (2v)= 1/2 × 5 × 82 = 160 J

Net work done W = ΔK = Kf - K= 180 - 40 J

W = 120 J

Hence the correct answer is option 4.

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