- Dr Sanjay Kumar Pawar

Reaction Distance, Braking Distance and Stopping Distance for NEET

Educational diagram showing stopping distance, reaction distance, braking distance, reaction time, braking time, and stopping distance formula for NEET Physics.

Stopping distance consists of reaction distance and braking distance, an important concept in NEET Physics.

Stopping Distance Notes - NEET Physics

Stopping Distance (Reaction Distance + Braking Distance)

Definition

Stopping distance is the total distance travelled by a vehicle from the moment the driver notices an obstacle until the vehicle comes to complete rest.

Stopping Distance = Reaction Distance + Braking Distance

S = sr + sb

1. Reaction Distance (Thinking Distance)

Reaction distance is the distance travelled by the vehicle during the driver's reaction time before applying the brakes.

Reaction Time

Reaction time is the time taken by the driver from observing an obstacle to applying the brakes.

Generally, Reaction Time < 1 second

Formula

sr = u × tr

Where,

sr = Reaction Distance
u = Initial Velocity
tr = Reaction Time

During reaction time:

Brakes are not applied.
Velocity remains constant.
Acceleration = 0

2. Braking Distance

Braking distance is the distance travelled after applying the brakes until the vehicle comes to rest.

During braking,

Vehicle decelerates.
Final velocity becomes zero.

Formula

v² = u² − 2as

Since

v = 0

Therefore,

sb = u² / 2a

Where

sb = Braking Distance
a = Deceleration

3. Stopping Distance Formula

S = ut_r + u² / 2a

This is the most important formula for NEET examinations.

4. Safe Distance

Safe distance is the minimum distance required between two vehicles to avoid collision.

Safe Distance ≥ Stopping Distance

5. Difference Between Reaction Distance and Braking Distance

Reaction Distance	Braking Distance
Before applying brakes	After applying brakes
Velocity remains constant	Velocity decreases
Acceleration = 0	Negative acceleration
Depends on reaction time	Depends on braking force

6. Important NEET Points

Reaction distance depends on speed and reaction time.
Braking distance depends on speed².
If speed doubles, braking distance becomes four times.
Stopping distance = Reaction distance + Braking distance.
Reaction time is usually less than 1 second.

7. Formula Sheet

Reaction Distance = u × tr

Braking Distance = u² / 2a

Stopping Distance = ut_r + u² / 2a

8. Practice Questions

Q1. A car moves with speed 20 m/s. Reaction time is 0.5 s. Find the reaction distance.

Answer: 20 × 0.5 = 10 m

Q2. A vehicle moves at 30 m/s. Braking deceleration is 5 m/s². Find braking distance.

Answer: 30² / (2 × 5) = 900 /10 = 90 m

Q3. A car travels at 25 m/s. Reaction time = 0.8 s Deceleration = 5 m/s² Find stopping distance.

Reaction Distance = 25 × 0.8 = 20 m
Braking Distance = 25² /10 = 62.5 m
Stopping Distance = 20 + 62.5
= 82.5 m

9. Multiple Choice Questions

During reaction time acceleration is
- A. Positive
- B. Negative
- C. Zero ✔
- D. Infinite
Reaction distance depends upon
- A. Speed
- B. Reaction time
- C. Both A and B ✔
- D. Braking force
Braking distance is proportional to
- A. Speed
- B. Speed² ✔
- C. Time
- D. Mass only
Stopping distance equals
- A. Reaction distance
- B. Braking distance
- C. Reaction distance + Braking distance ✔
- D. None
If speed doubles, braking distance becomes
- A. Double
- B. Half
- C. Four Times ✔
- D. Eight Times

10. One Minute Revision

✔ Reaction Distance = Before braking
✔ Braking Distance = After braking
✔ Stopping Distance = Reaction Distance + Braking Distance
✔ Reaction Distance = u × tr
✔ Braking Distance = u² / 2a
✔ Stopping Distance = ut_r + u² / 2a
✔ Braking Distance ∝ Speed²

Physics Teacher

Sunday, July 12, 2026