Class Notes NCERT Solutions for CBSE Students
Question: Classify the following as motion along a straight line, circular or oscillatory motion:
- Motion of your hands while running – Oscillatory motion
- Motion of a horse pulling a cart on a straight road – Straight line motion
- Motion of a child in a merry-go-round – Circular motion
- Motion of a child on a see-saw – Oscillatory motion
- Motion of the hammer of an electric bell – Oscillatory motion
- Motion of a train on a straight bridge – Straight line motion
Question: Which of the following are not correct?
Answer: 1) The basic unit of time is second – Correct
2) Every object moves with a constant speed – Not correct, Every object may or may not moves with a constant speed
3) Distances between two cities are measured in kilometers – Correct
4) The time period of a given pendulum is not constant – Not correct, Time period of a given pendulum is always constant because it depends on the length of the pendulum.
5) The speed of a train is expressed in m/h – Not correct, The speed of a train is measured in km/h or in m/s.
Question: A simple pendulum takes 32 s to complete 20 oscillations. What is the time period of the pendulum?
Answer: Numbers of oscillations = 20
Time taken = 32 sec
Time period of the pendulum = Time taken / Numbers of oscillations
= 32 / 20 = 1.6 s.
Question: The distance between two stations is 240 km. A train takes 4 hours to cover this distance. Calculate the speed of the train.
Answer: Distance between two stations = 240 km
Time taken = 4 hrs
Speed of train = Distance / Time taken
= 240 / 4 = 60 km / hr
Question: 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.
Answer: Initial reading of odometer = 57321.0 km
Final reading of odometer = 57336.0 km
Initial Time = 8:30 AM
Final Time = 8:50 AM
Total distance covered = Final reading of odometer – Initial reading of odometer
=57336.0 – 57321.0 = 15.0 km
Total time taken = Final Time – Initial Time
= 8:50 AM – 8:30 AM = 20 minutes
20 minutes = 20/60 hrs = 1/3 hrs
Speed of the car = Total distance covered/Total time taken = 15.0/20 = 0.75 km/min
Speed of the car in km/hr =15/(1/3) = 45 km/hr
Question: 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.
Answer: Speed of bicycle = 2 m/s
Time taken = 15 mins = 15 * 60 secs = 900 secs
As per question,
Speed = Distance/Time
= Distance = Speed * Time = 2 * 900 m = 1800 m = 1.8 km
Question: 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
Answer: Firstly, the car is moving with 40 km/h for 15 minutes.
15 minutes = 15/60 hrs = 1/4 hrs
Distance covered = 40 * 1/4 = 10 km
Secondly, the car is moving with 60 km/h for 15 minutes.
Distance covered = 60 * 1/4 = 15 km
Total distance covered = 10 km + 15 km = 25 km
