NDA (I) 2025 General Ability Test · Question 150 of 150

Correct — C, Zero. Acceleration is the rate of change of velocity. When a body moves at uniform speed along a straight line its velocity does not change in magnitude or direction, so the change in velocity is zero and therefore the acceleration is zero. (The one exception is motion in a curve, such as uniform circular motion, where the direction keeps changing and there is a centripetal acceleration even though the speed is constant — but for straight-line uniform speed the acceleration is zero.)

• (a)Maximum — Acceleration is largest when velocity changes most rapidly; at uniform speed the velocity is not changing at all, so it cannot be maximum.
• (b)Minimum — 'Minimum' is vague; the acceleration is not merely small but exactly zero when the speed is uniform in a straight line.
• (d)Constant — Zero is indeed a constant value, but the precise and intended answer is that the acceleration is zero, not simply some non-zero constant.

Speed is the magnitude of velocity; velocity also has direction. Acceleration is the rate of change of velocity, so a body accelerates only if its speed OR its direction changes. Moving at a steady speed in a straight line means constant velocity, hence zero acceleration. Uniform circular motion is the special case where speed is constant but direction changes, giving a non-zero (centripetal) acceleration.

The options tempt you with 'constant' (true in the trivial sense that zero is constant) and 'minimum'. The exact answer for uniform speed in a straight line is that the acceleration is zero, because the velocity is unchanging.

• Acceleration = change in velocity ÷ time; it is zero when velocity is constant.
• Uniform speed in a straight line means constant velocity and hence zero acceleration.
• On a velocity–time graph, uniform velocity is a horizontal line whose slope (acceleration) is zero.
• In uniform circular motion the speed is constant but a centripetal acceleration exists because the direction changes.

• Choosing 'constant' — although zero is constant, the intended answer is that acceleration is zero.
• Assuming constant speed always means zero acceleration; in circular motion direction changes, so there is centripetal acceleration.

Asked directly about acceleration at uniform speed, or by reading the slope of a velocity–time graph.

No directly related past PYQ was found.

• practice — not a real PYQ

  On a velocity–time graph, motion with zero acceleration is represented by

  • (a)a straight line sloping upward
  • (b)a horizontal straight line
  • (c)a curve bending upward
  • (d)a straight line sloping downward

  Answer(b) a horizontal straight line — constant velocity means zero slope, i.e. zero acceleration.

• practice — not a real PYQ

  A body moving in a circle at constant speed has

  • (a)zero acceleration
  • (b)acceleration directed towards the centre
  • (c)acceleration along its motion
  • (d)decreasing speed

  Answer(b) acceleration directed towards the centre — its direction changes, giving centripetal acceleration even at constant speed.