Ch- Motion , Subjective and Exemplar questions

 Motion

Subjective Questions

1. What is motion? Is motion absolute or relative? Illustrate with an example.

Motion is the change in position of a body with respect to time.
Motion is not absolute; it is relative.
Example: A passenger sitting in a moving bus is at rest relative to the bus, but in motion relative to a person standing on the road. ✅

2. What do you mean by time period of oscillation? How is it dependent on the length and mass of the simple pendulum?

The time period is the time taken to complete one oscillation.
For a simple pendulum, T = 2π√(L/g).
It depends on the length (L) of the pendulum, but not on the mass of the bob. ✅

3. How is average speed different from speed?

Speed is the distance covered per unit time.
Average speed is the total distance travelled divided by the total time taken. ✅

4. Distinguish between periodic and non-periodic motion.

Periodic motion: Motion repeated at equal intervals of time (e.g., pendulum).
Non-periodic motion: Motion not repeated at equal intervals of time (e.g., running boy). ✅

5. Differentiate between uniform motion and non-uniform motion.

Uniform motion: Equal distance covered in equal intervals of time (e.g., a car moving at constant speed).
Non-uniform motion: Unequal distance covered in equal intervals of time (e.g., bus in traffic). ✅

---

Numericals

1. A body travels from point A to B and returns to A by the same path. Length of AB = 15 km. Find distance covered.

Distance = AB + BA = 15 + 15 = 30 km ✅

2. A bus covers 80 km in 2 hours and 115 km in 3 hours. Find average speed.

Total distance = 80 + 115 = 195 km
Total time = 2 + 3 = 5 h
Average speed = 195 ÷ 5 = 39 km/h ✅

3. Manoj went to Pune, 120 km from Mumbai. He started at 5.00 am and reached at 7.00 am. Find average speed.

Distance = 120 km
Time = 2 h
Average speed = 120 ÷ 2 = 60 km/h ✅

4. Calculate frequency of a pendulum if time period is 2 seconds.

f = 1/T = 1/2 = 0.5 Hz ✅

5. Prerna moves in a circle of radius 7 m, Mita moves in a square of side 11 m. Compare distances for 1 round.

Prerna’s distance = 2πr = 2 × 3.14 × 7 ≈ 44 m
Mita’s distance = 4 × 11 = 44 m
Both cover equal distance. ✅

---

Exemplar Problems

1. Weight of an object varies from one place to other, but mass remains constant. Explain.

Mass is the amount of matter, independent of location.
Weight = mass × acceleration due to gravity. Since acceleration due to gravity changes with location, weight changes. ✅

2. X and Y are physical quantities. X is often used in place of Y in everyday conversation, Y can never be negative. Choose correct options.

X = Weight (often used in daily life as "mass")
Y = Mass (cannot be negative)
A = Negative (only weight can be negative as force direction). ✅

3. A car is travelling on a straight road. Identify motion of:

a) Axle → Rotational motion
b) Front wheels → Rotational + Translational
c) Seats → Translational
d) Rear wheels → Rotational + Translational ✅

4. Ramesh and Kamal weigh 20 kg of iron at pole and equator. Will their weights be same?

No, acceleration due to gravity is more at the poles than at the equator.
Thus, the same mass will weigh slightly more at the poles. ✅