Chapter 13: Motion and Time

Q.1.Identify the following actions:

(a)The hand movement when you are running.

(b) Pulling of cart by a cow on the road.

(c)Train motion on a straight bridge.

(d)The hammer motion in an electric bell.

(e)Motion of a child on a see-saw

(f)Motion of a child in a merry-go-round.

Ans. (a) Oscillatory motion

(b)Linear motion

(c) circular motion

(d)Oscillatory motion

(e) Oscillatory motion

(f)Linear motion

Q.2. Identify the wrong one:

(a)Second is the unit of time.

(b)The speed of all objects are same.

(c)Measurement of distance between two cities is in kilometers.

(d)The pendulum time period is not constant.

(e)The train speed is expressed in m/h

Ans. (b), (d), (e)

Q.3.A pendulum takes 40s to complete 25 oscillations. Find the pendulum’s time period.

Ans. Time taken to complete 40 oscillations = 40 s

Time taken to complete 1 oscillation= 40/25 s = 1.6 s

Time period of a pendulum is time taken by it to complete 1 oscillation.

Pendulum time period is 1.6 s.

Q.4. Two stations are 450km apart. A train takes 6hrs to cover this distance. What is the train’s speed?

Ans. Distance = 450 km

Time taken = 4 hrs

Speed = distance covered/time taken = 450km/6 hrs = 75km/hr

Train speed is 75 km/hr.

Q.5. A Car shows 57300.0km on its odometer when the time was 08.30 AM. What is the distance traveled by the car at 08.50 AM if the odometer reads 57400.0 km? During this time what is the speed of the car in km/min? Show the speed in km/hr.

Ans. Distance = 57400.0km – 57300 km=100 km

Speed in km/min = $$\frac{100}{20}$$ = 5 km/min

Speed in km/hr = $$\frac{100km}{\frac{1}{3}hr}$$

= 300 km/hr.

Q.6. By bicycle Kamal takes 20 minutes to reach his school from his house. If the speed of the bicycle is  4m/min. How far is his house and school apart?

Ans. Time taken = 20 min

Speed = 4 m/min

Distance = $$speed\ast time$$ = $$2\ast 15$$ = 80 m

Distance between Kamal’s house and school is 80 m.

Q.7. Draw the distance-time graph for the following case:

(a) A car moving at a constant speed.

(b) A car parked on a side road.

Ans.

Q.8.Which of the following is correct?

(a)Speed = $$distance\ast time$$

(b)Speed = $$\frac{distance}{time}$$

(c)speed = $$\frac{time}{distance}$$

(d)speed = $$\frac{1}{distance\ast time}$$

Ans. (ii) Speed = $$\frac{distance}{time}$$

Q.9.The unit of speed is:

(a) km/min (b) m/min (c) km/h (d) m/s

Ans. (d) m/s

Q.10. The speed of the car is 50 km/h for 20 minutes and then the speed is 100 km/h for the next 15 minutes. The car covered a distance of:

(a)20 (b) 37.5 (c) 37 (d) 40

Ans.

Speed of the car for first 15 minute = 50km/h

Speed of the car for next 15 minute = 100 km/h

15 minutes = $$\frac{15}{60}hrs$$ = 0.25 hrs

Distance = (Speed) X (Time)

Distance travelled in first 15 minute = 0.25 hour = 50 km/h X 0.25 hour = 12.5 km

Distance travelled in next 15 minute = 100 km/h X 0.25 hour = 25 km

Thus, total distance covered = 12.5 km + 25 km = 37.5 km

Therefore (b) is correct

Q.11.Two photographs are taken at an interval of 20 seconds. If a distance of 200 meters is shown by 1 cm in these photographs, then what is the speed of the blue car.

Ans. Distance covered by blue car should be measured.

The distance covered by car in meter is got from multiplying the distance measured in cm by 100 (i.e. 100 x distance measured)

Distance in meters is to be divided by 20 seconds. You will get the speed of the car in meters/second

Assume that the car’s distance is 3.5 cm.

Distance covered by car = 3.5 x 200 = 700 meter.

Time (given in question) = 20 second

Speed = $$\frac{Distance}{time}$$ = $$\frac{700m}{20s}$$

= 35 m/s

Therefore the speed of the car is 35 m/s.

Q.12.The distance-time graph for the motion of two vehicles X and Y are shown below. Which of the following moves fast?

Ans. As the slope of X is higher than the slope of Y in the distance-time graph, it is evident that vehicle X is moving fast as compared to vehicle Y

Q.13. Identify the one in which the truck is not moving with a constant speed from the given distance-time graph.

Ans. (C). Since the slope of the graph is not a straight line and keeps changing and is not uniform.

Practise This Question

1. megha
May 26, 2018

nobody attended the chat i had a question i waited for 5-6 min

2. Harshul Vashisht
March 7, 2018

Antony sir explain very well