9th Standard Chapter 7 Motion NCERT Exercise Questions with Answers

Motion Class – 9th Standard Mode

1. An athlete completes one round of a circular track of diameter 200 m in 40 s. What will be the distance covered and the displacement at the end of 2 minutes 20 s?

   Distance per lap = π × 200 m ≃ 628.3 m

   Total time = 2 min 20 s = 140 s ⇒ laps = 140 ÷ 40 = 3.5

   Total distance = 3.5 × 628.3 ≃ 2199.1 m

   Displacement = straight‐line from start to end. After 3½ laps you’re opposite the start ⇒ 200 m

2. Joseph jogs from A to B (300 m) in 2 min 30 s, then 100 m back to C in 1 min. Find average speed & velocity: a) A→B b) A→C

   a) A→B

   Distance = 300 m; Time = 150 s

   Speed = 300 ÷ 150 = 2.0 m/s

   Velocity = 300 ÷ 150 = 2.0 m/s

   b) A→C

   Total distance = 400 m; Total time = 210 s

   Speed = 400 ÷ 210 ≃ 1.90 m/s

   Displacement = 200 m; Velocity = 200 ÷ 210 ≃ 0.95 m/s

3. Abdul drives to school at 20 km/h and returns at 30 km/h. What is his average speed for the round trip?

   Let one‐way = D km. Time there = D/20 h; back = D/30 h ⇒ total time = D(1/20+1/30) = D/12 h

   Total distance = 2D ⇒ Average speed = 2D ÷ (D/12) = 24 km/h

4. A motorboat starts from rest, accelerates at 3 m/s² for 8 s. How far does it travel?

   u=0; a=3; t=8

   s=ut + ½at² = 0 + 0.5×3×8² = 96 m

5. A car at 52 km/h brakes. Shade the area under the speed–time curve for braking. Which part is uniform motion?

   The shaded area under the deceleration segment = distance during braking.

   The horizontal line at 52 km/h represents uniform motion.

6. Fig. 7.10: distance–time graph of A, B, C. a) Who’s fastest? b) Do any meet? c) How far has C gone when B passes A? d) How far has B gone when it passes C?

   a) Steepest slope ⇒ fastest.

   b) Intersections on the graph show meeting points.

   c) Read C’s y‐value at the time B crosses A.

   d) Read B’s y‐value at the time B crosses C.