Unit Test (Solutions): Motion and Time | Science Class 7 (Old NCERT) PDF Download

Time: 1 hour
Maximum Marks: 30
Attempt all questions.

• Question numbers 1 to 5 carry 1 mark each.
• Question numbers 6 to 8 carry 2 marks each.
• Question numbers 9 to 11 carry 3 marks each.
• Question numbers 12 & 13 carry 5 marks each.

Q1: What is the SI unit of speed?  (1 Mark)
(a) km/h
(b) m/s
(c) cm/s
(d) m/min
Ans: (b) m/s
The SI unit of speed is meters per second (m/s).

Q2: Define speed.  (1 Mark)
Ans: Speed is the distance covered by an object in unit time. It is given by:
Speed = Distance covered / Time taken

Q3: Which of the following is an example of uniform motion?  (1 Mark)
(a) A car moving on a busy road
(b) A bus stopping frequently for passengers
(c) A satellite moving around Earth at a constant speed
(d) A person jogging at varying speeds
Ans: (c)
Uniform motion occurs when an object moves in a straight line with constant speed.

Q4: How many seconds are there in one hour?  (1 Mark)
Ans: 3600 seconds
Since 1 hour = 60 minutes and 1 minute = 60 seconds,
60 × 60 = 3600 seconds

Q5: What is the function of a speedometer?  (1 Mark)
Ans: A speedometer measures and displays the speed of a vehicle in km/h.

Q6: Differentiate between uniform motion and non-uniform motion.  (2 Marks)
Ans:

• Uniform motion: An object moving at a constant speed in a straight line (e.g., a train moving at 60 km/h on a straight track).
• Non-uniform motion: The speed of an object keeps changing over time (e.g., a car in traffic stops and moves at different speeds).

Q7: Convert 36 km/h into m/s.  (2 Marks)
Ans: We use the conversion formula:
Speed in m/s = Speed in Km/h x (5/18)
= 36 x 5/18 = 10 m/s

Q8: A car moves with a speed of 30 km/h for 20 minutes. Find the distance covered by the car.  (2 Marks)
Ans: Distance = Speed x Time
Time in hours:
20 min = 20/60 hours = 1/3 hours
Distance = 30 x 1/3 = 10 km

Q9: Explain the working of a simple pendulum and define its time period.  (3 Marks)
Ans:

• A simple pendulum consists of a bob (a small, heavy object, often a metallic ball) suspended from a fixed point by a light, inextensible thread. When the bob is displaced slightly from its rest position and released, it moves to-and-fro about its mean position, exhibiting oscillatory motion due to the restoring force of gravity.
• Formula:
  

Q10: A cyclist covers 500 meters in 2 minutes. Find his speed in m/s and km/h.  (3 Marks)
Ans:
Speed = Distance / Time
Given: Distance = 500 meters,
Time = 2 minutes = $2\times 60=1202\; \backslash times\; 60\; =\; 120$
Speed in $m\mathrm{<br>}\backslash mathrm\{m\}/\backslash mathrm\{s$/s:
$Speed=\frac{500}{120}=4.1666\dots \approx 4.17m/s(rounded\; to\; 2\; decimal\; places)\backslash text\{Speed\}\; =\; \backslash frac\{500\}\{120\}\; =\; 4.1666\backslash ldots\; \backslash approx\; 4.17\; \backslash mathrm\{~m\}/\backslash mathrm\{s\}\; \backslash text\{\; (rounded\; to\; 2\; decimal\; places)\}$ (rounded to 2 decimal places)

Speed in $km/\mathrm{<br>}\backslash mathrm\{km\}/\backslash mathrm\{h\}$/h:
Convert $m\mathrm{<br>}$/s to $km/h\backslash mathrm\{km\}/\backslash mathrm\{h\}$ by multiplying by $\frac{18}{5}\backslash frac\{18\}\{5\}$  (since $1m/s=\frac{18}{5}km/h1\; \backslash mathrm\{~m\}/\backslash mathrm\{s\}\; =\; \backslash frac\{18\}\{5\}\; \backslash mathrm\{~km\}/\backslash mathrm\{h\}$ ):
$4.1666\dots \times \frac{18}{5}=15km/h(exact)4.1666\backslash ldots\; \backslash times\; \backslash frac\{18\}\{5\}\; =\; 15\; \backslash mathrm\{~km\}/\backslash mathrm\{h\}\; \backslash text\{\; (exact)\}$

Alternatively:

Distance in km = $500m=0.5km\; 500\; \backslash text\{\; m\}\; =\; 0.5\; \backslash text\{\; km\}$ km, Time in hours = $2min=\frac{2}{60}=\frac{1}{30}h\; 2\; \backslash text\{\; min\}\; =\; \backslash frac\{2\}\{60\}\; =\; \backslash frac\{1\}\{30\}\; \backslash text\{\; h\}$ h

$SpeedSpeed\; =\frac{0.5}{\frac{1}{30}}=0.5\times 30=15km/h\backslash text\{Speed\}\; =\; \backslash frac\{0.5\}\{\backslash frac\{1\}\{30\}\}\; =\; 0.5\; \backslash times\; 30\; =\; 15\; \backslash mathrm\{~km\}/\backslash mathrm\{h\}$

Final Answer: Speed = 4.17 $m\mathrm{<br>}\backslash mathrm\{m\}/\backslash mathrm\{s$/s, 15 $km\mathrm{<br>}\backslash mathrm\{km\}/\backslash mathrm\{h\}$/h.

Q11: Describe the difference between a speedometer and an odometer.  (3 Marks)
Ans:

• Speedometer: Measures instantaneous speed of a vehicle (shown in km/h).
• Odometer: Measures total distance traveled by a vehicle (shown in km).

Q12: Explain how to construct a distance-time graph and interpret its observations. (5 Marks)
Ans:
Steps to construct a distance-time graph:

1. Draw X-axis (Time) and Y-axis (Distance).
2. Choose a scale (e.g., 1 min = 1 cm for time, 1 km = 1 cm for distance).
3. Plot time vs. distance points.
4. Join points with a line.

Observations:

• Straight-line graph → Uniform motion
• Curved graph → Non-uniform motion
• Flat horizontal line → Object at rest
• Steep slope → Higher speed

Q13: A car moves with a speed of 50 km/h for 30 minutes and then with a speed of 80 km/h for 45 minutes. Find the total distance covered. (5 Marks)
Ans:
For 50 km/h:
Time = 30 min = 30 / 60 = 0.5 hours
Distance = 50 × 0.5 = 25 km

For 80 km/h:
Time = 45 min = 45 / 60 = 0.75 hours
Distance = 80 × 0.75 = 60 km

Total distance: 25 + 60 = 85 km