D. Tick (4) the odd-one out giving reason.
1. Periodic motion, Oscillatory motion, Vibratory motion, Random motion
Odd one out: Random motion
Reason: Periodic, oscillatory, and vibratory motions repeat themselves at regular intervals, whereas random motion does not follow a fixed pattern.
2. Sundial, Water clock, Stopwatch, Table clock
Odd one out: Stopwatch
Reason: A stopwatch measures short time intervals, while the others are used to show the time of the day.
3. Simple pendulum, Bob, Mean position of the bob, Balance wheel
Odd one out: Balance wheel
Reason: The simple pendulum, bob, and mean position of the bob are related to a pendulum, whereas a balance wheel is used in watches.
4. Speed, Metre per second, Speedometer, Odometer
Odd one out: Odometer
Reason: Speed, metre per second, and speedometer are related to speed, whereas an odometer measures distance travelled.
5.
Odd one out: third image
Reason:In all the other distance–time graphs, the distance either increases or remains constant as time increases.
The third graph shows distance decreasing with time, which is not possible in a distance–time graph because distance travelled by an object cannot decrease.
II. SHORT ANSWER TYPE QUESTIONS
1. When a body can said to be in motion ? Can any body be at absolute rest ?
Ans. A body is said to be in motion when it changes its position with time with respect to a fixed reference point.
No, no body can be at absolute rest.2. Name the device that is used for measuring time interval. Name the agency which provides time-keeping services in India.
Ans. A time interval is measured using a stopwatch or stop clock. Time-keeping services in India are provided by the National Physical Laboratory, New Delhi.
3. Under what condition, the time period of a pendulum does not depend upon the amplitude of oscillation ?
Ans. When the amplitude of oscillation is small, the time period of a pendulum does not depend on it.
4. Define speed. What is its SI Unit ?
Ans. The distance travelled by an object in unit time is defined as its speed. In other words,
Speed = Distance travelled / Time taken
The SI unit of speed is metre per second (m/s).
5. Define nonuniform motion. Give one example.
Ans. When a body travels unequal distances in equal intervals of time, it is said to be in non-uniform motion. The motion of a car on a hilly road is an example of non-uniform motion.
III. LONG ANSWER TYPE QUESTIONS
1. When is an object said to be in motion ?
Ans. When an object changes its positions with time it is said to be in motion.
2. Classify motion of the following as linear, circular and oscillatory motion.
(a) a cyclist on a straight plane road
(b) a plucked string of a sitar
(c) tip of the hand of a clock
(d) earth moving around the sun
(e) a stone falling from certain height
(f) a swing
Ans. (a) Linear
(b) Oscillatory
(c) Circular
(d) Circular (periodic)
(e) Linear
(f) Oscillatory
3. Describe (a) the time period and (b) amplitude of a simple pendulum.
Ans.(a) Time period : The time taken by the bob of a pendulum to complete one oscillation is called the time period of the pendulum. It is measured in second and denoted by T.
(b) Amplitude : The maximum displacement of the bob from its mean position on either
side is called amplitude of the pendulum. It is measured in metre and denoted by A.
4. Define average speed. What are its units ? How can it be measured ?
Ans. Average speed : The average speed of a moving body is equal to the total distance travelled by the body in unit time.
Average speed = Total Distance travelled / Total time taken
SI unit of average speed is m/s.
To measure average speed, we measure
(i) Total distance travelled by any object.
(ii) Total time taken by the object to cover the distance.
To measure the average speed of a moving ball:
1. Draw two parallel straight lines at a distance of 2-3 metres from each other.
2. Roll a ball gently from the line 1 towards line
2 and ask your friend to start the stopwatch at the same time. This is zero time.
3. Ask your friend to stop the stopwatch as soon as the ball reaches line 2. Read the time in
the stopwatch and note it down.
4. Measure the distance between the two lines. Note down the distance moved by the ball.
5. Repeat the experiment 3 – 4 times.
Average speed = Total Distance travelled / Total time taken
5. What is meant by uniform and non-uniform
motion ? What kind of motion is shown by the
following diagrams?
Ans. A body is said to have uniform motion when it travels equal distances in equal intervals of time.
A body is said to have nonuniform motion when it travels unequal distances in equal intervals of time.
Nonuniform motion is shown by the above graph.
IV. HIGHER ORDER THINKING SKILLS
1. The bob of a simple pendulum takes 0.25 s to go from one extreme position to the mean position. What is the time period of the pendulum ?
Ans. Time period of the pendulum is the time taken by it to complete one oscillation. The pendulum completes one oscillation when its bob, starting from its mean position O, moves to one extreme position to A, then to other extreme position B and then back to mean position O.
The time period of the pendulum = 0.25 × 4 = 1.00 second.
2. Draw the distance-time graph for a honeybee moving around a flower at a speed of 1m / min. Calculate the distance travelled by it in 0.50 min?
Ans. Since the honeybee is moving around the flower
in random motion, its distance time graph will
not be a straight line.
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