Exercise Questions
Question 1. Classify the following as motion along a straight line, circular or oscillatory motion:
(i) Motion of your hands while running.
(ii) Motion of a horse pulling a cart on a straight road.
(iii) Motion of a child in a merry-go-round.
(iv) Motion of a child on a see-saw.
(v) Motion of the hammer of an electric bell.
(vi) Motion of a train on a straight bridge.
Solution 1.
i) Motion of your hands while running- oscillatory
ii) Motion of a horse pulling a cart on a straight road- Motion along a straight line
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- Motion along a straight line.
Question 2. Which of the following is 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 constant.
(v) The speed of a train is expressed in m/h.
Solution 2. The following statements are not correct:
(ii) Every object moves with a constant speed.
(iv) The time period of a given pendulum is constant.
(v) The speed of a train is expressed in m/h.
Question 3. A simple pendulum takes 32 s to complete 20 oscillations. What is the time period of the pendulum?
Solution 3.
Number of oscillations = 20
Total time taken to complete 20 oscillations = 32 s
Question 4. The distance between the two stations is 240 km. A train takes 4 hours to cover this distance. Calculate the speed of the train.
Solution 4.
Distance between two stations = 240 kms
Total time take = 4 hrs./240 minutes
= 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 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 5.
The initial reading of the odometer = 57321.0
The final reading of the odometer = 57336.0
Distance covered by the car = Final reading of the odometer – Initial reading of the odometer
= 57336.0 – 57321.0 = 15 km
Starting time of the car is 8:30 and it stops at 8: 50
Hence, time is taken by car = 20 mins
= 45 km/h
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 6.
Time taken by Salma to reach her school by bicycle = 15 mins= 15 x 60 = 90 s
Speed of Salma’s bicycle= 2m/s
Speed = distance/time
Distance covered = speed x time taken
= 2 x 900 = 1800 m
1000m = 1 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 at a constant speed.
(ii) A car parked on a side road.
Solution 7.
Question 8. Which of the following relations is correct?
(i) Speed = Distance × Time
(ii) Speed = Distance/Time
(iii) Speed = Time/Distance
(iv) Speed = 1/Distance x Time
Solution 8.
Answer is (ii) Speed = Distance/Time
Question 9. The basic unit of speed is:
(i) km/min
(ii) m/min
(iii) km/h
(iv) m/s
Solution 9.
(iv) m/s
Question 10. A car moves at 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 10.
The answer is (ii) 25 km
Calculation:
When the speed of the car is 40 km/h
Time taken = 15 min = 15/60 = 0.25 h
Distance covered d1 = speed x time taken
= 40 x 0.25 = 10 km
When the speed of the Car is 60 km/ h
Distance covered d2 = speed x time taken
= 60 x 0.25= 15 km
Total distance covered by the car = d1 + d2
= 10 + 15
= 25 km
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 fastest car.
Solution:
The distance covered by the blue car from one horizontal white strip to another, which is measured by scale is 1.2 cm.
1 cm =100 m.
Therefore, 1.2 cm = 120 m.
Distance travelled by car = 120 m
Time taken to cover this distance = Time interval between the two photographs = 10 s
= 120/10
= 12 m/s
Question 12. Fig. 13.15 shows the distance-time graph for the motion of two vehicles A and B. Which one of them is moving faster?
Solution 12.
Vehicle A is moving faster than vehicle B.
Question 13. Which of the following distance-time graphs shows a truck moving with a speed which is not constant?
Solution 13.
iii) shows that a truck moving at a speed which is not constant.