Question

when a car driver travelling at a speed of 20m/s applies the brake and bring the car to rest in 4 sec the acceleration of the car will be​

Answer 1

Understanding the question: This question says that we have to find out the acceleration of the car if a car driver is travelling at a speed of 20 m/s and then he applies a brake and bring the car to rest in 4 seconds. Let's do it!

Given that:

• Initial velocity = 20 m/s

• Final velocity = 0 m/s

• Time taken = 4 seconds

Don't be confused! Final velocity came as zero because brake is applied after car is already travelling.

To calculate:

• The acceleration

Solution:

• The acceleration = -5 m/s²

Using concept:

• Formula to find acceleration

Using formula:

• ${\sf{a \: = \dfrac{v-u}{t}}}$

• a denotes acceleration, v denotes final velocity, u denotes initial velocity and t denotes time

Full solution:

$:\implies \sf a \: = \dfrac{v-u}{t} \\ \\ :\implies \sf a \: = \dfrac{0-20}{4} \\ \\ :\implies \sf a \: = \dfrac{-20}{4} \\ \\ :\implies \sf a \: = \cancel{\dfrac{-20}{4}} \: (Cancelling) \\ \\ :\implies \sf a \: = -5 \: ms^{-2} \\ \\ :\implies \sf Acceleration \: = -5 \: ms^{-2}$

Therefore, -5 m/s sq. is the acceleration of the car. Means the car retards as it's came in negative!

Answer 2

Explanation:

Here

• Initial velocity=u=20m/s
• Final velocity=v=0m/s
• Time=t=4s

We know that

$\boxed{\sf Acceleration=\dfrac{v-u}{t}}$

$\\ \sf\hookrightarrow Acceleration=\dfrac{0-20}{4}$

$\\ \sf\hookrightarrow \dfrac{-20}{4}$

$\\ \sf\hookrightarrow -5m/s^2$

$\\ \sf\hookrightarrow Retardation= -5ms^{-2}$