NCERT Textbook Exercises

Q1. Classify the following as motion along a straight line, circular or oscillatory motion:

(i) Motion of your hands while running: Oscillatory motion.
(ii) Motion of a horse pulling a cart on a straight road: Straight line motion.
(iii) Motion of a child in a merry-go-round: Circular motion.
(iv) Motion of a child on a see-saw: Oscillatory motion.
(v) Motion of the hammer of an electric bell: Oscillatory motion.
(vi) Motion of a train on a straight bridge: Straight line motion.

Q2. Which of the following are not correct?

(i) The basic unit of time is second. (Correct)
(ii) Every object moves with a constant speed. (Incorrect) (Speed can change).
(iii) Distances between two cities are measured in kilometres. (Correct)
(iv) The time period of a given pendulum is not constant. (Incorrect) (It is constant for a given length).
(v) The speed of a train is expressed in m/h. (Incorrect) (Usually km/h or m/s).

Q3. A simple pendulum takes 32 s to complete 20 oscillations. What is the time period of the pendulum?

Number of oscillations = 20
Total time taken = 32 s
Time period = Total time / No. of oscillations
= 32 / 20
= 1.6 seconds

Q4. The distance between two stations is 240 km. A train takes 4 hours to cover this distance. Calculate the speed of the train.

Distance = 240 km
Time = 4 h
Speed = Distance / Time
= 240 / 4
= 60 km/h

Q5. The odometer of a car reads 57321.0 km when the clock shows the time 08:30 AM. What is the distance moved by the car, if at 08:50 AM, the odometer reading has changed to 57336.0 km? Calculate the speed of the car in km/min during this time. Express the speed in km/h also.

Initial reading = 57321.0 km
Final reading = 57336.0 km
Distance covered = 57336.0 - 57321.0 = 15 km

Time taken = 8:50 AM - 8:30 AM = 20 min

Speed in km/min:
Speed = Distance / Time = 15 km / 20 min = 0.75 km/min

Speed in km/h:
Speed = 0.75 km/min * 60 min/h = 45 km/h

Q6. Salma takes 15 minutes from her house to reach her school on a bicycle. If the bicycle has a speed of 2 m/s, calculate the distance between her house and the school.

Time = 15 min = 15 * 60 = 900 s
Speed = 2 m/s
Distance = Speed * Time
= 2 * 900
= 1800 m
= 1.8 km

Q7. Show the shape of the distance-time graph for the motion in the following cases:

(i) A car moving with a constant speed: A straight line inclined to time axis.
(ii) A car parked on a side road: A straight line parallel to time axis.

Q8. Which of the following relations is correct?

(ii) Speed = Distance / Time

Q9. The basic unit of speed is:

(iv) m/s

Q10. A car moves with a speed of 40 km/h for 15 minutes and then with a speed of 60 km/h for the next 15 minutes. The total distance covered by the car is:

Case 1: Speed = 40 km/h, Time = 15/60 h = 1/4 h.
Distance 1 = 40 * 1/4 = 10 km.

Case 2: Speed = 60 km/h, Time = 15/60 h = 1/4 h.
Distance 2 = 60 * 1/4 = 15 km.

Total Distance = 10 + 15 = 25 km.
Answer: (ii) 25 km

Extra Important Questions

Q11. What is an Odometer?

The meter that measures the distance moved by the vehicle is called an odometer.

Detailed Chapter Topics

1. Types of Motion

Rectilinear: Along a straight line. (Car on straight road).
Circular: Along a circular path. (Hands of clock).
Oscillatory: To and fro motion. (Pendulum, Swing).
Periodic: Repeats after fixed interval of time. (Heartbeat, Motion of earth).

2. Speed

Distance covered by an object in unit time.
Formula: Speed = Total Distance / Total Time.
Non-Uniform Motion: Speed changes (moves fast then slow).
Uniform Motion: Speed remains constant.

3. Measurement of Time

Pendulum: A metallic ball (bob) suspended from a rigid stand.
Oscillation: One complete to and fro motion.
Time Period: Time taken to complete one oscillation.
Clocks use periodic motion to measure time.

4. Distance-Time Graph

A line graph.
Time on X-axis, Distance on Y-axis.
Straight Line: Indicates Uniform Motion (Constant Speed).
Parallel to Time Axis: Object is at Rest (Distance not changing).
Curved Line: Non-uniform speed.

Key Facts and Definitions

1. Units of Measurement

Time: Basic unit is second (s). Larger units: minute (min), hour (h).
Speed: Basic unit is metre per second (m/s). Other unit: km/h.
1 km/h = 5/18 m/s.

2. Quick Facts

Odometer: Measures distance moved by vehicle.
Speedometer: Measures speed of vehicle in km/h.
Quartz Clock: Modern clocks having an electric circuit with a cell. Much more accurate than pendulum clocks.
Galileo Galilei: Discovered that time period of a given pendulum is constant.

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