NEET Physics Question - Kinematics

A car is travelling at 72 kmh–¹ and is 20 m from a barrier when the driver puts on the brakes. The car hits the barrier 2s later. What is the magnitude of the constant deceleration?

\[7.2 ms^{-2}\]

\[10 ms^{-2}\]

\[36 ms^{-2}\]

\[15 ms^{-2}\]

Solution:

Given:
- Initial velocity: \( u = 20 \, \text{m/s} \)
- Time: \( t = 2 \, \text{seconds} \)
- Distance to the barrier: \( s = 20 \, \text{m} \)

Using the equation of motion:
\[
s = ut + \frac{1}{2} a t^2
\]
\[
20 = 20 \times 2 + \frac{1}{2} a \times 2^2
\]
\[
20 = 40 + 2a
\]
\[
2a = -20
\]
\[
a = -10 \, \text{m/s}^2
\]

Thus, the magnitude of the deceleration is 10 m/s².

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Solution:

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