MOTION IN A STRAIGHT LINE-QnA

Q1: What is motion?

Motion is said to occur when an object changes its position with time relative to a fixed reference point.

Q2: Is motion absolute or relative?

Motion is relative because it depends on the observer and the chosen frame of reference.

Q3: Define distance.

Distance is the total length of the actual path travelled by an object during motion.

Q4: Define displacement.

Displacement is the shortest straight-line distance between the initial and final positions with direction.

Q5: Can displacement be negative?

Yes, displacement can be negative depending on the chosen positive direction.

Q6: What is speed?

Speed is the rate at which an object covers distance with time.

Q7: What is velocity?

Velocity is the rate of change of displacement with respect to time.

Q8: Write SI unit of acceleration.

The SI unit of acceleration is metre per second squared.

Q9: What does zero acceleration indicate?

Zero acceleration means the velocity of the object remains constant.

Q10: What is uniform motion?

Uniform motion occurs when equal distances are covered in equal intervals of time.

Q11: Define retardation.

Retardation is acceleration acting opposite to the direction of motion.

Q12: What is free fall?

Free fall is motion under gravity alone, ignoring air resistance.

Q13: State the value of acceleration due to gravity.

The acceleration due to gravity near Earth is about \(9.8 m\ s^{-2}\).

Q14: What does slope of v–t graph show?

It represents the acceleration of the moving object.

Q15: What does area under v–t graph represent?

It gives the displacement covered by the object.

Q1: Distinguish between distance and displacement.

Distance is the total path length and is scalar, whereas displacement is the shortest path with direction and is vector.

Q2: Explain average speed.

Average speed is obtained by dividing total distance travelled by the total time taken.

Q3: Explain average velocity.

Average velocity is defined as total displacement divided by total time.

Q4: What is instantaneous velocity?

Instantaneous velocity refers to velocity at a particular instant of time during motion.

Q5: Why can velocity be zero while acceleration is non-zero?

At the highest point of vertical motion, velocity becomes zero but gravitational acceleration continues to act downward.

Q6: Explain uniform acceleration.

Uniform acceleration means velocity changes by equal amounts in equal time intervals.

Q7: Define reaction time.

Reaction time is the time taken by a person to respond to a stimulus such as braking.

Q8: What is stopping distance?

Stopping distance is the sum of reaction distance and braking distance of a vehicle.

Q9: State Galileo’s law of odd numbers.

Distances covered in successive equal time intervals are proportional to odd natural numbers.

Q10: Why are equations of motion limited in use?

They are valid only when acceleration remains constant throughout motion.

Q1: Explain motion of a body under free fall.

In free fall, an object moves solely under the influence of gravity. The acceleration remains constant and acts vertically downward throughout the motion. The velocity increases uniformly during descent and decreases uniformly during ascent. Free fall motion is independent of mass when air resistance is neglected, demonstrating the universal nature of gravitational acceleration.

Q2: Describe the velocity–time graph for uniformly accelerated motion.

For uniformly accelerated motion, the velocity–time graph is a straight line. The slope of this line represents acceleration, while the area under the graph between two time instants gives the displacement. This graphical approach helps visualize how velocity changes steadily with time.

Q3: Derive the expression for displacement in uniformly accelerated motion.

Starting from average velocity and assuming constant acceleration, displacement is obtained by multiplying average velocity with time, leading to the relation \(s = ut + \frac{1}{2}at^2\). This equation shows contributions from both initial velocity and acceleration.

Q4: Explain the stopping distance of vehicles in detail.

Stopping distance consists of reaction distance and braking distance. Reaction distance depends on driver alertness and speed, while braking distance depends on friction and speed squared. As speed increases, stopping distance increases rapidly, highlighting the importance of speed limits.

Q5: Explain the importance of sign convention in motion.

Sign convention helps define direction clearly in one-dimensional motion. Choosing a positive direction allows velocity, acceleration, and displacement to be assigned correct signs, ensuring accurate calculations and avoiding conceptual errors.

Q1: Discuss the motion of a body thrown vertically upward.

When a body is thrown upward, it moves against gravity and slows down uniformly. Its velocity decreases until it becomes zero at the highest point. After that, it accelerates downward with the same magnitude of acceleration, making the ascent and descent symmetrical in time.

Q2: Explain the equations of motion and their physical meaning.

The equations of motion mathematically relate displacement, velocity, acceleration, and time under constant acceleration. They help predict future motion and analyze past motion without knowing the cause of motion, forming the backbone of kinematics.

Q3: Describe the graphical analysis of motion.

Graphical analysis uses displacement–time and velocity–time graphs to study motion. Slopes and areas of these graphs provide velocity, acceleration, and displacement, making motion easier to interpret visually and mathematically.

Q4: Explain Galileo’s contribution to the study of motion.

Galileo introduced experimental methods and mathematical reasoning in motion studies. His law of odd numbers and emphasis on uniform acceleration laid the foundation for modern kinematics and scientific thinking in physics.

Q5: Why is the study of motion in a straight line important?

Motion in a straight line is the simplest form of motion. It builds the foundation for understanding more complex motion, dynamics, and real-life applications such as transportation and free fall.