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NEET Physics: conservation of mechanical energy Practice Questions

13 free multiple-choice questions on conservation of mechanical energy (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 particle is moving under gravity. If its kinetic energy is zero at a certain point, what is the potential energy of the particle at that point?

    • APositive
    • BNegative
    • CUndefined
    • DZero
    Show answer & explanation

    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.

  2. Q2. In a system where gravity is the only force acting, how is the change in mechanical energy related to the change in height?

    • AThe change in mechanical energy is equal to the change in potential energy only.
    • BThe change in mechanical energy is equal to the work done by gravity.
    • CThe change in mechanical energy is zero.
    • DThe change in mechanical energy is equal to the negative change in potential energy.
    Show answer & explanation

    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.

  3. Q3. A spring has a natural length of 10 cm. If it is stretched by 10 cm, the potential energy stored in the spring is: (Assume spring constant k=100 N/m)

    • A0.5 J
    • B50 J
    • C100 J
    • D10 J
    Show answer & explanation

    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.

  4. Q4. A ball is thrown vertically upward with an initial speed v₀. When the ball momentarily stops at its maximum height h, what is the mechanical energy of the ball at that point? (Neglect air resistance.)

    • Amgh
    • Bmgh - 1/2mv₀²
    • C1/2mv₀²
    • Dmgh + 1/2mv₀²
    Show answer & explanation

    Correct answer: D — mgh + 1/2mv₀²

    According to the law of conservation of mechanical energy, the total mechanical energy (Kinetic Energy + Potential Energy) remains constant. At the maximum height h, the velocity is zero (K=0), so the total energy is purely gravitational potential energy, E = mgh.

  5. Q5. A particle is moving in a conservative force field. Which statement correctly describes the mechanical energy of the particle?

    • AThe work done is always positive.
    • BThe kinetic energy changes with time.
    • CThe potential energy is constant.
    • DThe sum of kinetic energy and potential energy remains constant.
    Show answer & explanation

    Correct answer: D — The sum of kinetic energy and potential energy remains constant.

    In a conservative force field, the mechanical energy (the sum of kinetic energy (K) and potential energy (U)) is conserved. This means that the total mechanical energy remains constant throughout the motion.

  6. Q6. If the velocity of a moving object is doubled, assuming constant mass, its kinetic energy will be:

    • AHalved.
    • BIncreased by a factor of 2.
    • CDoubled.
    • DFour times.
    Show answer & explanation

    Correct answer: D — Four times.

    Kinetic energy is given by K = 1/2mv². If the velocity (v) is doubled to 2v, the new kinetic energy is K' = 1/2m(2v)² = 1/2m(4v²) = 4 (1/2mv²). Thus, the kinetic energy is quadrupled (four times).

  7. Q7. A simple pendulum swings. As the pendulum swings from its highest point (maximum height) to its lowest point, what happens to its mechanical energy?

    • AMechanical energy remains constant.
    • BKinetic energy increases, Potential energy decreases.
    • CKinetic energy and Potential energy are equal and constant.
    • DKinetic energy decreases, Potential energy increases.
    Show answer & explanation

    Correct answer: A — Mechanical energy remains constant.

    Since gravity is the only force doing work and it is a conservative force, the mechanical energy of the pendulum system is conserved throughout its swing, meaning it remains constant.

  8. Q8. Two objects are moving on a spring system where gravity is neglected. If one object moves with a higher velocity, its mechanical energy will be:

    • AHigher than the other object's energy.
    • BLower than the other object's energy.
    • CZero, as only kinetic energy is considered.
    • DEqual to the other object's energy.
    Show answer & explanation

    Correct answer: A — Higher than the other object's energy.

    Since the system is conservative (gravity neglected, no non-conservative forces), the total mechanical energy is conserved. If one object has higher kinetic energy (K = 1/2mv²), its total mechanical energy (E = K + U) must be higher than the other object's energy.

  9. Q9. If a body moves from a point A to a point B under the influence of gravity, the change in its mechanical energy is due to:

    • AThe work done by friction.
    • BThe change in potential energy.
    • CWork done by non-conservative forces.
    • DThe change in kinetic energy only.
    Show answer & explanation

    Correct answer: B — The change in potential energy.

    Since gravity is the only force considered conservative, the change in mechanical energy (ΔE) is equal to the negative change in potential energy (ΔU = -W₍non-conservative)). In this case, ΔE = -ΔU.

  10. Q10. A mass m moves along a curved path under gravity. If the path is conservative (only gravity acts), the change in kinetic energy is equal to the negative change in potential energy. This principle is known as:

    • AConservation of Mechanical Energy
    • BPrinciple of Momentum
    • CWork-Energy Theorem
    • DConservation of Linear Momentum
    Show answer & explanation

    Correct answer: A — Conservation of Mechanical Energy

    The statement that the change in kinetic energy equals the negative change in potential energy (or the change in total mechanical energy equals zero) is the definition of the Conservation of Mechanical Energy.

  11. Q11. A ball is thrown vertically upwards. As the ball moves from the ground to its highest point, what happens to its mechanical energy?

    • AIt becomes zero at the maximum height.
    • BIt decreases due to the work done by gravity.
    • CIt remains constant because gravity is a conservative force.
    • DIt increases because the ball is moving upwards.
    Show answer & explanation

    Correct answer: C — It remains constant because gravity is a conservative force.

    Since gravity is a conservative force and no non-conservative work is done, the total mechanical energy (Kinetic + Potential) is conserved throughout the motion.

  12. Q12. The principle of conservation of mechanical energy is directly related to which type of forces?

    • AConservative forces, such as gravity and spring force.
    • BNon-conservative forces like friction.
    • CForces that depend on velocity.
    • DForces that are non-zero only when displacement is zero.
    Show answer & explanation

    Correct answer: A — Conservative forces, such as gravity and spring force.

    Conservation of mechanical energy strictly applies when the only forces doing work are conservative forces (like gravity, elastic force). Non-conservative forces (like friction) change the total mechanical energy.

  13. Q13. A ball is thrown vertically upwards. At the highest point of its trajectory, its velocity is zero. What is the mechanical energy of the ball at this point?

    • AThe mechanical energy is half the initial kinetic energy.
    • BMaximum kinetic energy and zero potential energy.
    • CZero kinetic energy and maximum potential energy.
    • DOnly kinetic energy, as potential energy is zero.
    Show answer & explanation

    Correct answer: C — Zero kinetic energy and maximum potential energy.

    At the highest point, the velocity is zero, so Kinetic Energy (K) is zero. Since the height is maximum, Potential Energy (U) is maximum. Thus, the total mechanical energy is equal to the maximum potential energy.

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