**Motion and Time**

**Question 1.****Classify the following as motion along a straight line, circular or oscillatory motion :**

- Motion of your hands while running.
- Motion of a horse pulling a cart on a straight road.
- Motion of a child in a merry-go-round.
- Motion of a child on a see-saw.
- Motion of the hammer of an electric bell.
- Motion of a train on a straight bridge.

**Solution:**

- oscillatory
- straight line
- circular
- oscillatory
- oscillatory
- straight line.

**Question 2.****Which of the following are not correct?(i)** The basic unit of time is second.

**(ii)**Every object moves with a constant speed.

**(iii)**Distances between two cities are measured in kilometres.

**(iv)**The time period of a given pendulum is not constant.

**(v)**The speed of a train is expressed in m/h.

**Solution:****(ii) , (v).**

**Question 3.****A simple pendulum takes 32 s to complete 20 oscillations. What is the time period of the pendulum?**

**Solution:**

Time taken for 20 oscillations = 32 s

Time taken for 1 oscillation =

Hence, Time period = 1.6 s

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

**Solution :**Given, distance = 240 km,

time = 4 h,

speed = = = 60 km/h.

**Question 5.****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.**

**Solution:**

**Question 6.****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.**

**Solution:**

Given, Speed = 2 m/s

Time =15 min = 15 x 60 s = 900 s

distance = speed x time

= 2 m/s x 900 s = 1800 m

km

= 1.8 km

**Question 7.****Show the shape of the distance-time graph for the motion in the following cases :(i)** A car moving with a constant speed.

**(ii)**A car parked on a side road.

**Solution:****(i)** A car moving with a constant speed covers equal distance in equal intervals of time**(ii)** The distance-time graph of a car parked on a road side is such that with the increase in time, there is no change in distance.

**Question 8.****Which of the following relations is correct?(i)** Speed = Distance x Time

**(ii)**Speed =

**(iii)**Speed =

**(iv)**Speed =

**Solution:****(ii)** Speed =

**Question 9.**

The basic unit of speed is :**(i)** km/min**(ii)** m/min**(iii)** km/h**(iv)** m/s

**Solution:****(iv)** m/s

**Question 10.****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:(i)** 100 km

**(ii)**25 km

**(iii)**15 km

**(iv)**10 km

**Solution:****Distance travelled in first 15 min**

= speed x time

= 40 km/h x 15 min

= 40 km/h x 15/60 h = 10 km**Distance travelled in last 15 min**

= speed x time

= 60 km/h x 15 min

= 60 km/h x 15/60 h = 15 km

Total distance = (10 +15) km = 25 km

Hence, option (ii) is correct.

**Question 11.****Suppose the two photographs, shown in Fig. 13.1 and Fig. 13.2, had been taken at an interval of 10 seconds. If a distance of 100 metres is shown by 1 cm**in these photographs, calculate the speed of the blue car.

**Solution:**

Speed = 100 m/10 s = 10 m/s

**Question 12.****shows the distance-time graph for the motion of two vehicles A and B. Which one of them is moving faster?**

**Solution:**

Vehicle A is moving faster.

**Question 13.****Which of the following distance-time graphs shows a truck moving with speed which is not constant?**

**Solution:**

Graph (iii).