Motion and Time
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.
- straight line
- straight line.
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.
(ii) , (v).
A simple pendulum takes 32 s to complete 20 oscillations. What is the time period of the pendulum?
Time taken for 20 oscillations = 32 s
Time taken for 1 oscillation =
Hence, Time period = 1.6 s
The distance between two stations is 240 km. A train takes 4 hours to cover this distance. Calculate the speed of the train.
Given, distance = 240 km,
time = 4 h,
speed = = = 60 km/h.
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.
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.
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
= 1.8 km
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.
(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.
Which of the following relations is correct?
(i) Speed = Distance x Time
(ii) Speed =
(iii) Speed =
(iv) Speed =
(ii) Speed =
The basic unit of speed is :
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
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.
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.
Speed = 100 m/10 s = 10 m/s
shows the distance-time graph for the motion of two vehicles A and B. Which one of them is moving faster?
Vehicle A is moving faster.
Which of the following distance-time graphs shows a truck moving with speed which is not constant?