Lesson: Motion and Time

# Question: 1

Define motion.

## Solution:

The change in position of a body with respect to time is called motion.

# Question: 2

Write S.I. unit of speed and time.

## Solution:

S.I. unit of speed is metre per second (m/s) and S.I. unit of time is second (s).

# Question: 3

What is a speedometer?

## Solution:

It is a device that is used to measure the speed of the vehicle in km/h.

# Question: 4

Define time period of a simple pendulum.

## Solution:

The time taken by a simple pendulum to complete one oscillation is called its time period.

# Question: 5

Name any two ancient clocks that are used to measure time?

## Solution:

Sand clock and water clock

# Question: 1

Define distance and speed.

## Solution:

Distance: The distance covered by a moving object is the actual length of the path followed by the object.

Speed: Speed is the total distance covered divided by the total time taken.

# Question: 2

Define periodic motion and give an example.

## Solution:

When an object repeats its motion after an equal interval of time, this type of motion is called periodic motion.

Example: Motion of a simple pendulum

# Question: 3

What is odometer? What is its function?

## Solution:

It is a device that records total distance covered by the vehicle. It is used in vehicles to calculate the distance travelled in a particular journey.

# Question: 4

Define oscillation? On which factor does the time period of a pendulum depend?

## Solution:

The pendulum completes one oscillation when its bob moves from one extreme position A to the other extreme position B and comes back to A.

The time period of a simple pendulum depends on the length of the pendulum.

# Question: 5

Express 72 km/h in m/s.

## Solution:

72 km/h =  20 m/s

# Question: 6

The distance between two stations is 120 km. A train takes 2 hours to cover this distance. Calculate the speed of the train.

## Solution:

Distance travelled= 120 km

Time taken = 2 h

Speed =

$=\frac{120}{2}=$ 60 km/h

# Question: 1

What are the different types of motion?

## Solution:

Rectilinear motion: Motion of an object along a straight line is called a rectilinear motion. Example $–$ A parade

Circular motion: Motion of an object along a circular path is called a circular motion. Example $–$ A spinning top

Oscillatory motion: The to and fro motion of an object is called an oscillatory motion. Example $–$ A simple pendulum

Periodic motion: The motion of an object that is repeated at regular interval is called a periodic motion. Example $–$ Revolution of Earth around the Sun

# Question: 2

The odometer of a car reads 5500.0 km when the clock shows the time 06:30 p.m. What is the distance moved by the car, if at 06:50 p.m., the odometer reading has changed to 5530.0 km? Calculate the speed of the car in km/h for this duration.

## Solution:

Distance travelled by the car between 06:30 p.m. and 06:50 p.m.

= 5530.0 km − 5500.0 km

= 30 km

Time taken by the car to cover that distance

= 06:50 p.m. − 06:30 p.m.

= 20 m

= 20/60 h

= 1/3 /h

Speed of the car in km/min

Speed of the car in km/h

# Question: 3

A simple pendulum takes 20 seconds to complete 5 oscillations. Calculate the time taken by the pendulum to complete 20 oscillations.

## Solution:

The time taken by a pendulum to complete 5 oscillations = 20sec

The time taken by the pendulum to complete 1 oscillation $=\frac{25}{5}=$ 4 sec

Therefore, the time taken by the pendulum to complete 20 oscillations $=20×4=\text{\hspace{0.17em}}80\text{\hspace{0.17em}}\mathrm{sec}$

# Question: 4

The given figure represents distance-time graph. Answer the following questions.

(a)               What is the distance covered after 8 sec?

(b)               Calculate the speed of the object between 12 s and 20 s.

## Solution:

(a)               The distance covered by the object after 8 second is 4 m.

(b)               Distance travelled between 12th sec and 20th sec

.

Time interval

Speed =  $=\frac{2}{8}=$ 0.25 m/s