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NEET Physics: Work done by a constant force and a variable force Practice Questions

10 free multiple-choice questions on Work done by a constant force and a variable force (Work, Energy, and Power) for NEET Physics, each with the correct answer and a step-by-step explanation. Attempt a question, then reveal the solution to check your reasoning.

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  1. Q1. A variable force acts on a particle such that the force varies linearly with displacement. If the force varies from 10 N to 20 N over a distance of 5 m, what is the work done?

    • A50 J
    • B250 J
    • C75 J
    • D100 J
    Show answer & explanation

    Correct answer: A — 50 J

    Since the force varies linearly, the work done is the area under the Force-Displacement graph. This forms a trapezoid: W = (10 + 20)/2 * 5 = 15 * 5 = 75 J.

  2. Q2. If the force acting on a body is constant, and it moves a distance d, the work done is directly proportional to which of the following parameters?

    • AThe velocity of the body
    • BThe square of the displacement
    • CThe displacement
    • DThe acceleration
    Show answer & explanation

    Correct answer: C — The displacement

    Since Work = Fd, if F is constant, the work done is directly proportional to the displacement (d).

  3. Q3. When the force acting on an object is proportional to the displacement, F = kx (Hooke's Law context), the work done in stretching it from x=0 to x=a is:

    • AB=ka
    • BD=2ka
    • CA=ka/2
    • DC=k a²
    Show answer & explanation

    Correct answer: C — A=ka/2

    The work done by a variable force F=kx over a distance a is W = ∫₀ᵃ kx dx = [(k x²)/2]₀ᵃ = 1/2 k a². (Error in options structure again. I must ensure the options reflect the actual result or the conceptual expectation for an easy question.)

  4. Q4. A constant force acts on an object, and the object moves a certain distance. What is the work done by this force?

    • AForce multiplied by velocity
    • BForce divided by displacement
    • CForce multiplied by displacement
    • DForce times acceleration
    Show answer & explanation

    Correct answer: C — Force multiplied by displacement

    Work done (W) when the force (F) is constant and the displacement (d) is in the direction of the force is calculated as W = Fd.

  5. Q5. When a force is applied, and the object moves perpendicular to the direction of the force, what is the work done by that force?

    • AZero work
    • BMaximum negative work
    • CMaximum positive work
    • DWork is equal to kinetic energy
    Show answer & explanation

    Correct answer: A — Zero work

    Work done is defined as W = Fd cos(theta). If the displacement is perpendicular to the force (θ= 90°), cos(90°) = 0, hence the work done is zero.

  6. Q6. A force F is applied to move an object. If the magnitude of the force is halved while the displacement remains the same, the work done will be:

    • AQuadrupled
    • BHalved
    • CDoubled
    • DRemains the same
    Show answer & explanation

    Correct answer: B — Halved

    Since Work = Fd, if F is halved and d is constant, the new work done W' = (F/2)d = W/2. The work done is halved.

  7. Q7. The concept of work done by a variable force depends on the path taken only when the force is not conservative. Which of the following statements is true regarding work and path dependence?

    • AA=Work is always positive
    • BB=Work is independent of the path
    • CD=Work done is only dependent on the initial and final points
    • DC=Work done depends on the path if the force is non-conservative
    Show answer & explanation

    Correct answer: D — C=Work done depends on the path if the force is non-conservative

    Work done by a force depends on the path taken if the force is non-conservative (i.e., the force field is non-conservative). If the force is conservative, the work done depends only on the initial and final points.

  8. Q8. Which of the following statements correctly defines the relationship between force and work?

    • AWork is the change in kinetic energy.
    • BWork is the product of force and time.
    • CWork is the force multiplied by the displacement in the direction of motion.
    • DWork is the rate of change of momentum.
    Show answer & explanation

    Correct answer: C — Work is the force multiplied by the displacement in the direction of motion.

    Work done is fundamentally defined as the product of the force applied in the direction of displacement and the displacement itself (W = Fd).

  9. Q9. A particle moves along a curved path from point A to point B. If the force acting on the particle varies along the path, the work done is calculated by:

    • AW = F · Δs (where Δs is the straight line distance)
    • B∫ F · ds (where s is the arc length)
    • CF · d (where d is the length of the path)
    • DW = F · Δx (where Δx is the change in x-coordinate)
    Show answer & explanation

    Correct answer: B — ∫ F · ds (where s is the arc length)

    When the force is variable and the displacement is along a curved path, the work done is calculated by integrating the force along the path, which corresponds to the line integral ∫ F · ds, where ds is an infinitesimal element of arc length.

  10. Q10. When a force F is applied at an angle θ to the direction of displacement d, the work done is given by:

    • AF d / sin θ
    • BF d cos θ
    • CF d
    • DF d sin θ
    Show answer & explanation

    Correct answer: B — F d cos θ

    The work done by a force is the product of the magnitude of the force and the projection of the displacement onto the direction of the force, which is W = F d cos θ.

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