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A. Choose the correct option.

1. The time period of a simple pendulum depends on the
   a. length of the string
   b. mass of the bob
   c. extent to which the bob is displaced
   d. none of the above
   Answer: a. length of the string
2. What is the SI unit of time?
   a. second
   b. Minute
   c. Hour
   d. Day
   Answer: a. second
3. A toy took 20 seconds to cover a distance of 40 metres. What is its speed?
   a. 0.5 m/s
   b. 5 m/s
   c. 2 m/s
   d. 20 m/s
   Answer: c. 2 m/s
4. The distance travelled by a vehicle is displayed by the
   a. speedometer
   b. odometer
   c. distance-time graph
   d. pie chart
   Answer: b. odometer

B. Fill in the blanks with the correct words.

1. (Light year/kilometres per hour)  is a unit of time.
   Answer: Light Year 

• An hourglass is a type of  (cup/clock).
  Answer: clock
• The time period of a pendulum depends on  or  is the SI unit of speed.
  Answer: length of the string, Metre per second
• In uniform motion, speed  (steadily increases/remains the same).

Answer: remains the same

C. Match the Following.

Item	Answer
1. Second	a. instrument to measure time
2. Clock	b. flat distance-time graph
3. Pendulum	c. SI unit of time
4. Zero speed	d. measured in m/s or km/h
5. Speed	e. periodic motion

Item	Answer
1. Second	c. SI unit of time
2. Clock	a. instrument to measure time
3. Pendulum	e. periodic motion
4. Zero speed	b. flat distance-time graph
5. Speed	d. measured in m/s or km/h

D. Answer the following questions.

1. Name three instruments used to measure time.
   Answer: Clock, Watch, and Hourglass.
2. Explain the use of periodic motion to measure time.
   Answer: Periodic motion repeats at regular intervals. By counting these consistent cycles, we can measure elapsed time, as seen in the swinging of a pendulum in a clock.
3. Name two units of time larger than a day.
   Answer: Week and Month.
4. Name one clock that uses the movement of the sun to keep time.
   Answer: Sundial.
5. What is speed? Give its SI unit.
   Answer: Speed is the distance travelled by an object per unit of time. Its SI unit is metre per second (m/s).

E. Numerical Problems.

1. A vehicle travels 25 km in 15 minutes. Calculate its speed in km/h.

Solution:

• Distance travelled = 25 km
• Time taken = 15 minutes
• First, convert time to hours (since the required speed unit is km/h).
  Time in hours = 15 minutes ÷ 60 minutes/hour = 0.25 hours
• Speed = Distance ÷ Time
• Speed = 25 km ÷ 0.25 h
• Speed = 100 km/h

Final Answer: 100 km/h

2. A commercial aircraft travels at 900 km/h. Calculate the distance it travels in 5 hours.

Solution:

• Speed of aircraft = 900 km/h
• Time taken = 5 hours
• Distance travelled = Speed × Time
• Distance = 900 km/h × 5 h
• Distance = 4500 km

Final Answer: 4500 km

3. Seismic waves (earthquake waves) travel at about 8 km/s on the Earth’s crust. Calculate the distance it travels in 10 s.

Solution:

• Speed of seismic waves = 8 km/s
• Time taken = 10 s
• Distance travelled = Speed × Time
• Distance = 8 km/s × 10 s
• Distance = 80 km

Final Answer: 80 km

4. Convert the following

a. 30 s to minutes

Solution:

• 1 minute = 60 seconds
• Therefore, minutes = Seconds ÷ 60
• Minutes = 30 ÷ 60
• Minutes = 0.5

Final Answer: 0.5 minutes

b. 72 hours to days

Solution:

• 1 day = 24 hours
• Therefore, days = Hours ÷ 24
• Days = 72 ÷ 24
• Days = 3

Final Answer: 3 days

c. 90 km/h to m/s

Solution:

• To convert km/h to m/s, multiply by (1000 m / 3600 s) which is equal to (5/18).
• Speed in m/s = 90 × (5/18)
• Speed in m/s = (90 ÷ 18) × 5
• Speed in m/s = 5 × 5
• Speed in m/s = 25

Final Answer: 25 m/s

d. 75 m/s to km/h

Solution:

• To convert m/s to km/h, multiply by (3600 s / 1000 m) which is equal to (18/5).
• Speed in km/h = 75 × (18/5)
• Speed in km/h = (75 ÷ 5) × 18
• Speed in km/h = 15 × 18
• Speed in km/h = 270

Final Answer: 270 km/h