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Motion in a Straight Line — NEET & JEE MCQs with answers
Kinematics of rectilinear (one-dimensional) motion is developed through the concepts of instantaneous velocity, speed and acceleration, their reading from position–time and velocity–time graphs, and the kinematic equations of uniformly accelerated motion, which relate displacement, time, initial velocity, final velocity and acceleration.
Topics in this chapter
- 2.1 Introduction
- 2.2 Instantaneous Velocity and Speed
- 2.3 Acceleration
- 2.4 Kinematic Equations for Uniformly Accelerated Motion
Free practice questions
A ball dropped from rest from 90 m ($g = 9.8\ \text{m s}^{-2}$) hits the floor at $42\ \text{m s}^{-1}$. At each collision it loses one tenth of its speed. Its speed just after the first collision is:
- A. $4.2\ \text{m s}^{-1}$
- B. $37.8\ \text{m s}^{-1}$
- C. $41.9\ \text{m s}^{-1}$
- D. $46.2\ \text{m s}^{-1}$
Show answer
Answer: B — Losing one tenth of 42 m s$^{-1}$ leaves $\tfrac{9}{10} \times 42 = 37.8\ \text{m s}^{-1}$. $4.2$ is the speed lost, not the speed left; $41.9$ subtracts 0.1 m s$^{-1}$ instead of one tenth; $46.2$ adds one tenth.
NCERT Class 11 Physics · Ch 2 · 2.4 Kinematic Equations for Uniformly Accelerated Motion
A particle moves with $x = 20 - 3.0\,t^{2}$ (SI units). What is its instantaneous speed at $t = 2\,\text{s}$?
- A. 24 m s$^{-1}$
- B. -12 m s$^{-1}$
- C. 12 m s$^{-1}$
- D. 6 m s$^{-1}$
Show answer
Answer: C — $v=dx/dt=-2\times3.0\times t=-6.0t$, so at $t=2$ s, $v=-12.0\,\text{m s}^{-1}$. Instantaneous speed is the magnitude: $|-12.0|=12.0\,\text{m s}^{-1}$.
NCERT Class 11 Physics · Ch 2 · 2.2 Instantaneous Velocity and Speed
According to the NCERT introduction, which two concepts are developed in order to describe motion?
- A. Momentum and impulse
- B. Force and energy
- C. Mass and weight
- D. Velocity and acceleration
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Answer: D — NCERT: 'In this chapter, we shall learn how to describe motion. For this, we develop the concepts of velocity and acceleration.' Hence velocity and acceleration are the concepts developed to describe motion.
NCERT Class 11 Physics · Ch 2 · 2.1 Introduction
For a particle moving in the negative direction with negative acceleration (Fig. 2.3c), its speed:
- A. increases
- B. decreases
- C. stays constant
- D. is zero throughout
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Answer: A — In Fig. 2.3(c), an object moving in the negative direction with a negative acceleration is speeding up (velocity becomes more negative, so speed increases).
NCERT Class 11 Physics · Ch 2 · 2.3 Acceleration
Two objects $200\,$m apart approach each other at $15\,$m s$^{-1}$ (A) and $5\,$m s$^{-1}$ (B). How far does **A** travel before they meet?
- A. 150 m
- B. 100 m
- C. 50 m
- D. 160 m
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Answer: A — Meeting time $t=d/(v_A+v_B)=200/20=10\,$s. Distance by A $=v_A\,t=15\times10=150\,$m.
NCERT Class 11 Physics · Ch 2 · 2.4 Kinematic Equations for Uniformly Accelerated Motion
A particle in one-dimensional motion has zero speed at a certain instant. Its velocity at that instant:
- A. may be non-zero if its acceleration is non-zero
- B. must be zero, because speed is the magnitude of velocity
- C. must be negative, because the particle is about to turn back
- D. can have any value, since speed and velocity are unrelated
Show answer
Answer: B — Instantaneous speed is the magnitude of velocity (p.15), so zero speed means zero velocity. A non-zero acceleration at that instant is possible (Points to Ponder 4, p.23), but it does not make the velocity non-zero; a velocity of exactly zero is neither negative nor positive; and speed and velocity are directly related.
NCERT Class 11 Physics · Ch 2 · 2.2 Instantaneous Velocity and Speed
The set of simple equations obtained for rectilinear motion with uniform acceleration is described in the NCERT introduction as relating to which motion condition?
- A. Motion only in two dimensions
- B. Uniform acceleration along a straight line
- C. Zero displacement at all times
- D. Continuously varying acceleration along a curve
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Answer: B — NCERT: 'For the case of rectilinear motion with uniform acceleration, a set of simple equations can be obtained.' The key condition is uniform acceleration along a straight line.
NCERT Class 11 Physics · Ch 2 · 2.1 Introduction
The average acceleration is the average change of velocity per unit:
- A. distance
- B. mass
- C. time
- D. area
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Answer: C — Average acceleration is the average change of velocity per unit time.
NCERT Class 11 Physics · Ch 2 · 2.3 Acceleration
Two objects $360\,$m apart approach each other at $24\,$m s$^{-1}$ (A) and $16\,$m s$^{-1}$ (B). How far does **A** travel before they meet?
- A. 144 m
- B. 216 m
- C. 180 m
- D. 226 m
Show answer
Answer: B — Meeting time $t=d/(v_A+v_B)=360/40=9\,$s. Distance by A $=v_A\,t=24\times9=216\,$m.
NCERT Class 11 Physics · Ch 2 · 2.4 Kinematic Equations for Uniformly Accelerated Motion
According to the NCERT introduction, water is described as flowing down a:
- A. Pipeline only
- B. Mountain peak
- C. Glacier
- D. Dam
Show answer
Answer: D — NCERT: 'water flowing down a dam.' Hence water is described as flowing down a dam, an example of motion.
NCERT Class 11 Physics · Ch 2 · 2.1 Introduction
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