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Measurement of Time and Motion – Class 7 Science notes, important questions and MCQs

NCERT Class 7 Science, chapter 8. Notes, key terms, important questions with answers and MCQs.

Chapter overview

Speed tells how fast something moves. We measure time with clocks and pendulums, and show motion using distance–time graphs.

Time and speed

Time period of a simple pendulum is the time for one complete oscillation; it is constant for a given length.
Speed = distance / time; SI unit m/s; also km/h.
Uniform motion: equal distances in equal times; non-uniform otherwise.

Graphs and devices

Distance–time graph: a straight sloping line means uniform speed; steeper line means faster.
Speedometer shows speed; odometer shows distance travelled.
1 km/h = 5/18 m/s.

Key terms

Oscillation: one complete to-and-fro motion of a pendulum
Uniform motion: covering equal distances in equal intervals of time
Odometer: instrument showing distance travelled by a vehicle

Formulas

Speed = distance / time
km/h × 5/18 = m/s

Important questions with answers

What is uniform motion? Give an example.2 marks

Motion in a straight line with constant speed, covering equal distances in equal intervals of time, e.g. a train moving steadily on a straight track.

A simple pendulum makes 20 oscillations in 32 seconds. Find its time period.3 marks

Time period = 32/20 = 1.6 s.

A bus travels 60 km in the first hour, 40 km in the next hour and 80 km in the third hour. Find its average speed. Is its motion uniform? What do a speedometer and an odometer show?5 marks

Total distance = 180 km, total time = 3 h, average speed = 60 km/h. The motion is non-uniform because different distances are covered in equal times. A speedometer shows the speed at that instant (km/h); an odometer shows the total distance travelled (km).

Quick revision

Speed = distance ÷ time.
Pendulum time period depends on length.
Steeper graph = faster.

Exam tips

Keep units the same before dividing.
A horizontal distance–time graph means the object is at rest.

Practice MCQs

SI unit of speed is
1. km/h
2. m
3. m/s
4. s
Show answer
Answer: (c) m/s. Metres per second.
A car covers 120 km in 2 hours. Its speed is
1. 240 km/h
2. 122 km/h
3. 60 km/h
4. 30 km/h
Show answer
Answer: (c) 60 km/h. 120 ÷ 2.
36 km/h in m/s is
1. 10 m/s
2. 36 m/s
3. 3.6 m/s
4. 100 m/s
Show answer
Answer: (a) 10 m/s. 36 × 5/18.
A pendulum makes 20 oscillations in 40 s. Its time period is
1. 20 s
2. 2 s
3. 0.5 s
4. 800 s
Show answer
Answer: (b) 2 s. 40 ÷ 20.
A car covers 150 km in 3 hours. Its speed is
1. 450 km/h
2. 30 km/h
3. 50 km/h
4. 153 km/h
Show answer
Answer: (c) 50 km/h. 150/3.
A distance–time graph is a horizontal line. The object is
1. moving fast
2. slowing down
3. speeding up
4. at rest
Show answer
Answer: (d) at rest. Distance does not change.
A bus travels 30 km in 30 minutes and then 30 km in 60 minutes. Its average speed is
1. 30 km/h
2. 45 km/h
3. 40 km/h
4. 60 km/h
Show answer
Answer: (c) 40 km/h. 60 km ÷ 1.5 h.
72 km/h in m/s is
1. 7.2 m/s
2. 20 m/s
3. 36 m/s
4. 259 m/s
Show answer
Answer: (b) 20 m/s. × 5/18.

All chapters of Class 7 Science

Written by Kundali IQ from standard, well-established facts to help with revision. This is not an official NCERT publication; always read your textbook too.