Physics Numericals - Motion & Weight | Class 7

Key Formulas Used:
- Average Speed = Total Distance / Total Time
- Weight = Mass × g, where g on Earth = 10 m/s²
- 1 kgf = 10 N when g = 10 m/s²
- Unit Conversion: 1 km/h = 5/18 m/s

1. Car's Average Speed

Q: A car covers 160 km in 4 h. What is the average speed?
Solution:
Average Speed = Distance / Time = 160 km / 4 h = 40 km/h

2. Train Travel Time

Q: A train travels 300 km at 60 km/h. How much time does it take?
Solution:
Time = Distance / Speed = 300 km / 60 km/h = 5 hours

3. Distance Covered by Boy

Q: A boy travels at 10 m/s for 20 min. How much distance?
Solution:
Time = 20 min = 20 × 60 = 1200 s
Distance = Speed × Time = 10 m/s × 1200 s = 12,000 m or 12 km

4. Boy's Motion & Average Speed

Q: A boy walks 30 m in 1 min and 30 m in 1.5 min. Type of motion? Average speed in m/s?
Solution:
Speed₁ = 30/60 = 0.5 m/s, Speed₂ = 30/90 = 0.33 m/s
Since speed changes → Non-uniform motion
Total Distance = 60 m, Total Time = 60 + 90 = 150 s
Average Speed = 60 / 150 = 0.4 m/s

5. Cyclist's Average Speed

Q: Cyclist travels 1 km, 0.5 km, 0.3 km in 1st, 2nd, 3rd hour. Find average speed in (i) km/h (ii) m/s
Solution:
Total Distance = 1.8 km, Total Time = 3 h
(i) Average Speed = 1.8 / 3 = 0.6 km/h
(ii) In m/s = 0.6 × 5/18 = 0.167 m/s

6. Car's Total Distance & Average Speed

Q: Car at 30 km/h for 30 min, then 40 km/h for 1 h. Find (a) total distance (b) total time (c) average speed
Solution:
(a) Distance₁ = 30 × 0.5 = 15 km, Distance₂ = 40 × 1 = 40 km → Total = 55 km
(b) Total Time = 0.5 + 1 = 1.5 hours
(c) Average Speed = 55 / 1.5 = 36.67 km/h

7. Weight of Boy on Earth

Q: On earth 1 kg weight = 10 N. Find weight of 37 kg boy in (a) kgf (b) N
Solution:
(a) 1 kgf = 10 N, so 37 kg = 37 kgf
(b) Weight = 37 × 10 = 370 N

8. Mass & Weight on Moon

Q: 6 kg on moon = 10 N. If a boy of 30 kg goes to moon, find (a) mass (b) weight
Solution:
(a) Mass never changes → 30 kg
(b) g on moon = 10/6 = 1.67 m/s²
Weight = 30 × 1.67 = 50 N

Hope this helps! Drop a comment if you need LONG ANSWER TYPE QUESTIONS too.