Work & Energy — Set 1

Correct Answer: C. Joule

Work is measured in joule in the SI system. Work is done when a force causes displacement along its direction. The same unit is also used for energy in mechanics.

Correct Answer: A. 50 J

Use W = F s cosθ and here θ = 0°, so cosθ = 1. So W = 10 x 5 x 1 = 50 J. Positive work increases the object’s energy in that direction.

Correct Answer: D. Four times

Kinetic energy is KE = (1/2)mv^2, so it depends on v squared. Doubling v makes v^2 four times. Therefore kinetic energy becomes four times.

Correct Answer: C. When force is perpendicular to displacement

Work is W = F s cosθ, so it depends on the angle between force and displacement. If θ = 90°, cosθ = 0 and work becomes zero. A common example is centripetal force in uniform circular motion.

Correct Answer: B. 200 W

Power is the rate of doing work, so P = W/t. Here P = 600/3 = 200 W. Power tells how fast energy is transferred.

Correct Answer: C. Double

Gravitational potential energy is PE = mgh. If h doubles, m and g stay the same, so PE doubles. Potential energy depends on the chosen reference level.

Correct Answer: A. 0°

Work is W = F s cosθ, so it is maximum when cosθ is maximum. The maximum value of cosθ is 1 at θ = 0°. Then the force acts fully along the displacement.

Correct Answer: A. Depends only on initial and final positions

A conservative force does work that depends only on the initial and final positions. The path taken between the points does not matter for such forces. Gravity is a common example of a conservative force.

Correct Answer: D. 9 J

Use KE = (1/2)mv^2 with m = 2 and v = 3. So KE = (1/2) x 2 x 9 = 9 J. Kinetic energy is always non-negative for real mass and speed.

Correct Answer: D. Change in its kinetic energy

The work-energy theorem links force and motion through energy. It states that net work done equals the change in kinetic energy. This helps solve problems without using time directly.