# NCERT Solution class 7 Science Chapter-13

__Chapter – 13 Motion and Time __

__Chapter Exercise __

__Page no. – ()__

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__Q.1__**– ****Classify the following as motion along a straight line, circular or oscillatory motion:-**

**Motion your hands while running.****Motion of a horse pulling a cart on a strait road.**

**iii. 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.**

** **

__Ans.1__**– **

**Oscillator Motion.****Linear Motion.**

iii. Circular Motion.

- Oscillatory Motion.
- Oscillatory Motion.
- Linear Motion.

__Q.2__**– Which of
**

**the following are not correct?**

**The basic unit of a time is second.****Every object moves with a constant speed.**

**iii. Distancing between two cities are measuring in kilometer.**

**The time period the given pendulum is constant.****The speed of a train is expressed by m/h.**

** **

__Ans.2__**– **The following statements are in correct:-

- Every object moves with a constant speed.
- The time period the given pendulum is constant.
- The speed of a train is expressed by m/h.

__Q.3__**– A simple pendulum takes 32 s to complete 20 oscillation. What is the period of pendulum. **

** **

__Ans.3__**– **

**Total Number of The Oscillation –****Total time taken to complete 20 Oscillation –**32 s.

**Time Period = **____Total time taken____

Number of oscillation

= ____32________ = 1.6 s

20

__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.4__**– **

**The distance between two stadium =**240 km.**Total time taken =**4 hours

**Speed = __ Distance__**

** Time **

**Speed = **____240________ = 60

4

= 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.5__**– **

**The Initial reading of the odometer =**0.**The Final reading of the odometer =**0.

**Formula, **

**Distance covered by the car = Final reading – Initial Reading **

**= **57336 – 57321. 0 = 15 km.

**The car’s starting time =**8:30 AM**The car’s stop time =**8:50 AM**So, Total time taken =**20 minutes.**Total Distance =**15 km.

**Speed = __ Distance covered__**

** Time taken **

** = __**__15________ = 0.75

20

= 0.75 km/ min.

**Now, **

**1 Hour =**60 Minutes.**20 minutes =**___1___

** **3

**Speed = __ Distance covered__**

** Time taken **

** = **____15________ = 45

1/3

= 45 km/ h.

__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/ s, calculate the distance between her house and the school.**

** **

__Ans.6__**– **

**Time Taken by Salma =**15 Minutes**Speed of Cycle =**2 m/ s.**Minute convert into second =**15 * 60

** = **90 Sec.

**Speed =** ____Distance Covered____

Time Taken

**Distance =** Speed * Time

**Distance = **2 * 900 = 1800

1000 = 1

1800 = ____1____ * 1800 = 1.8

1000

= 1.8 kms

__Q.7__**– Show the shape of the distance – time graph for the motion in the following cases: **

**A car moving with a constant speed.****A car parked on a side road.**

__Ans.7__**– **i.-

ii.-

__Q.8__**– Which of the following regulations is correct? **

**Speed = Distance * Time****Speed = __**__Distance____

** Time**

**iii. Speed = __ Time__**

** Distance**

**Speed = ______**__1_________

** Distance * Time**

** **

__Ans.8__**– ii. **Speed = ____Distance____

Time

__Q.9__**– The basic unit of speed is:**

**km/ h****m/ min**

**iii. km/ h**

**m/ s**

** **

__Ans.9__**– **iv. m/ s.

__Q.10__**– A car moves with 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:- **

**100 km****25 km**

**iii. 15 km**

**10 km**

** **

__Ans.10__**– **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.11__**– Speed = 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? **

**Fig. 13.15 Distance – time graph for the motion of two cars**

** **

__Ans.12__**– **The Car ‘A’ is moving fast.

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

__Ans.13__**– iii.**