CBSE Class 7 Science Time Motion and Speed Assignment

Question 1. Here are a few units of time. Arrange them in a ascending order Second, day, year, month, munutes, hour
........... < ............ < ............... < ............... < ............ < .............
Answer: Second < Minutes < Hour < Day < Month < Year
In simple words: Units of time are arranged from the smallest duration to the largest duration.

Exam Tip: Remember standard time conversions: 1 minute = 60 seconds, 1 hour = 60 minutes, 1 day = 24 hours.

Question 2. Let us calculate your speed of walking.
Distance Travelled = .................... metres
Time taken = .................... sec.
Speed = \(\frac{\text{Distance Travelled}}{\text{Time taken}}\)
Speed = ------------------- = .................... m/sec.
(Note - you can do this activity in your school's corridor with the help of your friend)
Answer:
Distance Travelled = 50 metres
Time taken = 25 sec.
Speed = \(\frac{50}{25} = 2\) m/sec.
In simple words: Speed is calculated by dividing the total distance covered by the time taken to cover that distance.

Exam Tip: Always include proper SI units (m/sec or m/s) with your final numerical answer for speed.

Question 3. A simple pendulum takes 10s to complete 20 oscillations. What is the time period of the pendulum?
No. of oscillations = .................--------
Time taken = ........................ sec.
Time period of the pendulum = \(\frac{\text{Time taken}}{\text{No. of Oscillations}}\)
Time period of the pendulum = --------------------- = ............... s
Answer:
No. of oscillations = 20
Time taken = 10 sec.
Time period of the pendulum = \(\frac{10}{20} = 0.5\) s
In simple words: The time period is the time taken by a pendulum to complete one full oscillation.

Exam Tip: Time period is always defined as time divided by the number of oscillations, measured in seconds.

Question 4. Match the following
Column I (Distance-Time Graphs):
i) Horizontal straight line parallel to time axis
ii) Straight line inclined at an angle to time axis
iii) Curved line
Column II:
A) A car moving with a constant speed.
B) A car parked on a side road
C) A car moving with a speed changing
Answer:
Matchings:
- (i) matches with (B) A car parked on a side road.
- (ii) matches with (A) A car moving with a constant speed.
- (iii) matches with (C) A car moving with a speed changing.
In simple words: The shape of a distance-time graph tells us whether an object is stationary, moving at a steady speed, or accelerating.

Exam Tip: A straight inclined line in a distance-time graph always indicates uniform (constant) speed.

Question 4 a). Observe this bar graph showing runs scored by a team in each over and answer the following questions.
a) No. of runs scored in the 3rd over.
b) No. of runs scored in the 6th over.
Answer:
a) No. of runs scored in the 3rd over = 8 runs
b) No. of runs scored in the 6th over = 12 runs
In simple words: Read the height of the bar corresponding to each specific over on the horizontal axis.

Exam Tip: Carefully check the scale of the vertical axis before reading values from a bar graph.

Question 5. Observe this line graph showing change in weight of a man with age.
Age (in year)
a) Weight at the age of 10 yrs.
b) Weight at the age of 16 yrs.
Answer:
a) Weight at the age of 10 yrs = 30 kg
b) Weight at the age of 16 yrs = 55 kg
In simple words: Locate the age on the horizontal axis, move vertically up to the line graph, and read the corresponding weight on the vertical axis.

Exam Tip: Follow grid lines carefully from both axes to find the exact intersecting point on a line graph.

A. Answer in not more than 20 words.

1. What is a unit of measurement?

2. How are stopwatches different from ordinary watches?

3. What property of a pendulum made it suitable to b used in the manufacture of clocks?

4. What is the time period of a pendulum?

5. What is oscillation?

6. When a body is said to be in uniform motion?

7. Correct the following.

(a) 100 m.

(b) 50 kgs

(c) 20 secs

(d) 80 kilos

B. Numericals

1. A car takes 20 minutes to cover a distance of 15 km. calculate its speed in km/hr and m/s.

2. Plot s distance-time graph foe a body travelling at s speed of 1.5 m/s.

3. The distance between two towns is 600 km. how much time it would take to cover this distance at an average speed of 40 km/hr.

4. A man driving at an average speed of 45 km/hr takes 7 hours to travel from one town to another. What is the distance between the towns?