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A student said, “The Earth moves around the Sun”. In this context, discuss whether an object kept on the Earth can be considered to be at rest.
An object kept on the Earth can be considered at rest with respect to the Earth because its position remains unchanged relative to the Earth. However, the Earth itself moves around the Sun. Therefore, the same object is also moving relative to the Sun. Thus, whether an object is at rest or in motionRead more
An object kept on the Earth can be considered at rest with respect to the Earth because its position remains unchanged relative to the Earth. However, the Earth itself moves around the Sun. Therefore, the same object is also moving relative to the Sun. Thus, whether an object is at rest or in motion depends on the reference point or frame of reference chosen.
For more NCERT Solutions of Class 9 Science Exploration Chapter 4 Describing Motion Around Us Question Answer (2026-27)
https://www.tiwariacademy.com/ncert-solutions/class-9/science/exploration-chapter-4/
See lessA bus is travelling at 36 km h⁻¹ when the driver sees an obstacle 30 m ahead. The driver takes 0.5 seconds to react before pressing the brake. Once the brake is applied, the velocity of the bus reduces with constant acceleration of 2.5 m s⁻². Will the bus be able to stop before reaching the obstacle?
The initial speed is 36 km h⁻¹ = 10 m s⁻¹. During the reaction time of 0.5 s, distance travelled = 10 × 0.5 = 5 m. Braking distance is given by v² = u² + 2as: 0 = 100 − 5s, so s = 20 m. Therefore, total stopping distance = 5 + 20 = 25 m. Since the obstacle is 30 m away, the bus stops 5 m before it.Read more
The initial speed is 36 km h⁻¹ = 10 m s⁻¹. During the reaction time of 0.5 s, distance travelled = 10 × 0.5 = 5 m. Braking distance is given by v² = u² + 2as: 0 = 100 − 5s, so s = 20 m. Therefore, total stopping distance = 5 + 20 = 25 m. Since the obstacle is 30 m away, the bus stops 5 m before it.
For more NCERT Solutions of Class 9 Science Exploration Chapter 4 Describing Motion Around Us Question Answer (2026-27)
https://www.tiwariacademy.com/ncert-solutions/class-9/science/exploration-chapter-4/
See lessA car starts from rest and accelerates uniformly to 20 m s⁻¹ in 5 seconds. It then travels at 20 m s⁻¹ for 10 seconds and finally applies the brake (with uniform acceleration) to stop in 6 seconds. Find the total distance travelled.
The car first accelerates from 0 to 20 m s⁻¹ in 5 s. Distance travelled = ½(u + v)t = ½(0 + 20) × 5 = 50 m. It then travels at 20 m s⁻¹ for 10 s: distance = 20 × 10 = 200 m. During braking, distance = ½(20 + 0) × 6 = 60 m. Therefore, total distance = 50 + 200 + 60 = 310 m. For more NCERT SoluRead more
The car first accelerates from 0 to 20 m s⁻¹ in 5 s. Distance travelled = ½(u + v)t = ½(0 + 20) × 5 = 50 m. It then travels at 20 m s⁻¹ for 10 s: distance = 20 × 10 = 200 m. During braking, distance = ½(20 + 0) × 6 = 60 m. Therefore, total distance = 50 + 200 + 60 = 310 m.
For more NCERT Solutions of Class 9 Science Exploration Chapter 4 Describing Motion Around Us Question Answer (2026-27)
https://www.tiwariacademy.com/ncert-solutions/class-9/science/exploration-chapter-4/
See lessA truck driver driving at the speed of 54 km h⁻¹ notices a road sign with a speed limit of 40 km h⁻¹ for trucks. He slows down to 36 km h⁻¹ in 36 s. What was the distance travelled by him during this time? Assume the acceleration to be constant while slowing down.
Given, initial speed u = 54 km h⁻¹, final speed v = 36 km h⁻¹, and time t = 36 s = 0.01 h. Since acceleration is constant, average speed = (u + v)/2 = (54 + 36)/2 = 45 km h⁻¹. Therefore, distance travelled = average speed × time = 45 × 0.01 = 0.45 km = 450 m. For more NCERT Solutions of ClassRead more
Given, initial speed u = 54 km h⁻¹, final speed v = 36 km h⁻¹, and time t = 36 s = 0.01 h. Since acceleration is constant, average speed = (u + v)/2 = (54 + 36)/2 = 45 km h⁻¹. Therefore, distance travelled = average speed × time = 45 × 0.01 = 0.45 km = 450 m.
For more NCERT Solutions of Class 9 Science Exploration Chapter 4 Describing Motion Around Us Question Answer (2026-27)
https://www.tiwariacademy.com/ncert-solutions/class-9/science/exploration-chapter-4/
See lessA graph in Fig. 4.28 shows the change in position with time for two objects A and B moving in a straight line from 0 to 10 seconds. Choose the correct option(s). (i) The average velocity of both over the 10 s time interval is equal since they have the same initial and final positions. (ii) The average speeds of both over the 10 s time interval are equal since both cover equal distance in equal time. (iii) The average speed of A over the 10 s time interval is lower than that of B since it covers a shorter distance than B in 10 seconds. (iv) The average speed of A over the 10 s time interval is greater than that of B since B’s speed is lower than A’s in some segments.
The correct options are (i) and (ii). Both A and B start from the same position and reach the same final position, so their average velocities are equal. Since both objects move in the same direction and cover the same total distance during the 10-second interval, their average speeds are also equalRead more
The correct options are (i) and (ii). Both A and B start from the same position and reach the same final position, so their average velocities are equal. Since both objects move in the same direction and cover the same total distance during the 10-second interval, their average speeds are also equal. Options (iii) and (iv) are incorrect because their average speeds are equal.
For more NCERT Solutions of Class 9 Science Exploration Chapter 4 Describing Motion Around Us Question Answer (2026-27)
https://www.tiwariacademy.com/ncert-solutions/class-9/science/exploration-chapter-4/
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