**NCERT Solutions Class 7 Science Chapter 13 Motion and Time**

**Q.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.**

**Ans.**(i) Oscillatory motion

(ii) Linear motion

(iii) Circular motion

(iv) Oscillatory motion

(v) Oscillatory motion

(vi) Linear motion

**Q.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 kilometers. **

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

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

**Ans.** (ii), (iv), (v)

**Q.3.A simple pendulum takes 32s to complete 20 oscillations, what is the time period of the pendulum?**

**Ans**. Time taken to complete 20 oscillations = 32 s

Time taken to complete 1 oscillation = 32/20 s = 1.6 s

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

Time period of pendulum is 1.6 seconds.

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

**Ans.**Distance = 240 km

Time taken = 4 hours

Speed =Distance covered/time taken = 240km/4 hammer

=60 km/h

Speed of train =60 km/h

**Q.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.**

**Ans**.Distance = 57336.0 km – 57321 km =15 km

Speed in km/min =15km/20 min = 3/4 km/min

Speed in km/hr =15 km/1/3 hr

=(15 x 3) km/hr

=45 km/hr.

**Q.6.Salma takes 15 minutes from her house to reach her school on a bicycle. If the bicycle has a speed of 2 m/min, calculate the distance between her house and the school.**

**Ans**.Time taken =15 min

Speed = 2 m/min .

Distance = speed x time = 2 x 15 = 30 m

Distance between Salma’s school and her house is 30 m.

**Q.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**

**Ans.
**

**Q.8. Which of the following relations is correct?**

**(i) Speed = Distance Time**

**(ii) Speed = Distance/Time**

**(iii)Speed – Time/Distance**

**(iv)Speed = 1/Distance Time**

**Ans.** (ii) Speed = Distance/Time is correct

**Q.9.The basic unit of speed is:**

**(i) km/min (ii) m/min (iii) km/h (iv) m/s**

**Ans**. (iv) m/s

**Q.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**

**Ans.**(ii) 25 km

**Q.11.Suppose the two photographs, shown in fig. 13.1 and fig. 13.2 of NCERT 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.**

**Ans.**0.1 cm/s or 10 m/s

**Q.12.Fig 13.10 shows the distance-time graph for the motion of two vehicles A and B. Which one of them is moving faster?**

**Ans**. ‘A’ is moving faster.

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

**Ans**. (iii)

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