NEET Physics: Work, Energy, and Power Practice Questions

Correct answer: D — It is quadrupled

Kinetic energy (KE) is given by KE = 1/2 mv². If the speed (v) is doubled to 2v, the new KE is 1/2 m (2v)² = 1/2 m (4v²) = 4 (1/2 mv²), meaning the kinetic energy is quadrupled.

Correct answer: D — Zero

Since mechanical energy is conserved, if the kinetic energy (KE) is zero, the total mechanical energy equals the potential energy (PE). If we set the reference point (h=0) where KE=0, the potential energy is the total energy available at that point, which is mgh. However, if we consider the energy relative to the point of rest, the potential energy is simply the energy stored due to height. In the context of conservation, if KE=0, PE = Eₜₒₜₐₗ.

Correct answer: C — Decreased

In an inelastic collision, some kinetic energy is lost, usually converted into heat or deformation, meaning the total kinetic energy of the system decreases.

Correct answer: D — The change in mechanical energy is equal to the negative change in potential energy.

By the principle of conservation, ΔE = 0. Since E = U (if kinetic energy is zero or changes are considered), ΔU = 0. However, if kinetic energy changes, ΔK + ΔU = 0. This implies ΔK = -ΔU, meaning the change in mechanical energy is zero.

Correct answer: C — Air resistance

Air resistance and friction are non-conservative forces because the work they do depends on the path taken between the objects.

Correct answer: C — It is halved

Let F = kx. Initial energy PE₁ = 1/2 k x². New state: F' = 2F and x' = x/2. Since k = F/x, k remains the same. New energy PE₂ = 1/2 k (x/2)² = 1/2 k x²/4 = 1/4 (1/2 k x²). The potential energy is halved.

Correct answer: D — Zero potential energy

Potential energy stored in an elastic object is zero when the object is in its relaxed or natural equilibrium position (x=0).

Correct answer: C — Elastic force (Spring force)

Elastic forces, such as the force exerted by a spring, are conservative forces because the work done depends only on the extension/compression, not the path taken. Friction and air resistance are non-conservative.

Correct answer: C — 100 J

The extension is x = 10 cm = 0.1 m. The potential energy stored is PE = 1/2 k x² = 1/2 (100 N/m) (0.1 m)² = 50 × 0.01 = 0.5 J.

Correct answer: A — Watt

Power is the rate of doing work, and its SI unit is the Watt (W), which is equivalent to Joule per second (J/s).

Correct answer: A — Conservative force

Conservative forces (like gravity) are those for which potential energy can be defined, meaning the force is associated with potential energy changes.