Students can Download Science Chapter 13 Motion and Time Questions and Answers, Notes Pdf, KSEEB Solutions for Class 7 Science helps you to revise the complete Karnataka State Board Syllabus and to clear all their doubts, score well in final exams.

## Karnataka State Syllabus Class 7 Science Chapter 13 Motion and Time

### Class 7 Science Motion and Time Textbook Exercise Questions and Answers

Question 1.

Classify the following as motion along a straight line, circular or oscillatory motion:

- The motion of your hands while running,
- The motion of a horse pulling a cart on a straight road,
- The motion of a child in a merry – go – round.
- The motion of a child on a see-saw.
- The motion of the hammer of an electric bell.
- The motion of a train on a straight bridge.

Answer:

- Oscillatory motion
- Straight-line motion
- Circular motion
- Oscillatory motion
- Oscillatory motion
- Straight-line motion.

Question 2.

Which of the following are not correct?

- The basic unit of time is second.
- Every object moves at a constant speed.
- Distances between two cities are measured in kilometers.
- The time period of a given pendulum is constant.
- The speed of a train is expressed in m/h.

Answer:

- Correct
- Not correct
- Correct
- Not correct
- Not correct

Question 3.

A simple pendulum takes 32S to complete 20 oscillations. What is the time period of the pendulum?

Answer:

Time is taken = 32 seconds.

Number of oscillations = 20

Time period = ?

\(\text { Time period. }=\frac{\text { Total time taken }}{\text { Number of oscillations }}\)

\(=\frac{32}{20}=\frac{16}{10}=1.6\) Seconds

∴ The time period of the pendulum is 1.6 seconds.

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.

Answer:

Distance between two stations = 240 km

Time taken = 4 hr

∴ \(\text { Speed }=\frac{\text { Total distance }}{\text { Time taken }}=\frac{240}{4}\) = 60 km/hr

∴ The speed of the train is 60 km per hour.

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.

Answer:

Initial reading = 57321.0 km

Final reading = 57336.0 km

Total distance covered by the car = 57336 – 57321 = 15 km

Initial time = 08.30 AM

Final time =08.50 AM

Time taken = 20 min

\(Speed =\frac{\text { Total distance covered }}{\text { Time taken }}\)

\(=\frac{15}{20}=\frac{3}{4}\) km per minute = 0.75 x 60 = 45 km/hr

∴ The speed of the car is 45 km per hour.

Question 6.

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

Answer:

Time taken = 15 min = 15 x 60 = 900sec

Speed of the bicycle = 2 m / sec

Distance = Speed x time taken

= 2 x 900

= 1800m

= 1.8 km

∴ The distance between Salma’s house and the school is 1.8 km.

Question 7.

Show the shape of the distance-time graph for the motion in the following cases:

(a) A car moving at a constant speed.

(b) A car parked on a side road.

Answer:

(a) A car moving with a constant speed covers equal distance in equal intervals of time.

(b) A car parked on a side road does not change in distance with an increase in time.

Question 8.

Which of the following relations is correct?

(a) Speed = Distance x Time

(b) Speed = \(\frac{\text { Distance }}{\text { Time }}\)

(c) Speed = \(\frac{\text { Distance }}{\text { Time }}\)

(d) Speed = \(\frac{1}{\text { Distance } \times \text { Time }}\)

Answer:

(b) Speed = \(\frac{\text { Distance }}{\text { Time }}\)

Question 9.

The basic unit of speed is

(a) km/m in

(b) ni/min

(c) km/h

(d) m/s

Answer:

(d) m/s

Question 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:

(a) 100 km

(b) 25 km

(c) 15 km

(d) 10 km

Answer:

(b) 25 km

Question 11.

Suppose the two photographs, shown below 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.

Answer:

The distance covered by the car from one strip to another, which is measured by scale is 1.4 cm.

Given, 1 cm is equivalent to 100 m

∴ 1.4 cm is equivalent to = 1.4 x 100 = 140 m

∴ Distance travelled by the car = 140 m

Time interval between the two photographs = 10 s

∴ Speed = \(\frac{\text { Distance covered }}{\text { Time taken }}=\frac{140}{10}\) = 14 m/s

Thus, the speed of the fastest car is 14 m/s.

Question 12.

The figure shows the distance-time graph for the motion of two vehicles A and B. Which one of them is moving faster?

Distance – time graph for the motion of two cars.

Answer:

Speed = \(\frac{\text { Distance covered }}{\text { Time taken }}\)

This relation shows that the speed of a vehicle is greater if it covers maximum distance at a given interval of time. The distance covered is compared by drawing a line perpendicular to the time axis.

At a given time t, the distance covered by vehicle A is more than vehicle B.

Hence, vehicle A is moving faster than vehicles.

Question 13.

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

Answer:

(c) The graph shows that a truck is moving with a speed which is not constant.