Question

A driver applies brakes to decrease the speed of the bus from 45km/hr to 10km/hr in 6 seconds. Find the acceleration of the car.

Answer 1

Given :

• Initial Velocity(u) = 45 km/hr

• Final Velocity (v) = 10 km/hr

• Time = 6 seconds

To Find :

• Acceleration of the car

Solution :

First of all convert the given Velocity into their proper unit.

For Converting km/hr into m/s we've to multiply the unit with $\sf\dfrac{5}{18}$

● 45 km/hr

→ 45 × $\sf\dfrac{5}{18}$

→12.5 m/s

● 10 km/hr

→ 10 × $\sf\dfrac{5}{18}$

→ 2.78 m/s

Let's find Acceleration now :

We know that,

$\dag \: \: \boxed{ \sf \: Acceleration = \frac{Change \: in \: Velocity}{Time \: taken} }$

$\rightarrow \: \: \boxed{ \sf \: Acceleration = \dfrac{Final \: Velocity -Initial \: Velocity }{Time \: taken} }$

$\bigstar \: \: \large \: \boxed{ \sf \: a = \frac{v - u}{t}}$

$\longrightarrow \sf \: a = \dfrac{2.78 - 12.5}{6}$

$\longrightarrow \sf \: a = \cancel \dfrac{ - 9.72}{6}$

$\longrightarrow \sf \red{a = - 1.62}$

$\therefore$ Acceleration of the car is -1.62ms⁻¹

Answer 2

convert km into m of both

45 km/h = 45 x 1000/3600 = 45x 10/36 = 12.5 m/s

10 km/h = 10 x 1000/3600 = 10 x 10/36 =2.7 m/s

data : u = 12.5m/s , v = 2.7 m/s , t = 6s

a = v - u / t

a = 2.7 - 12.5 / 6 = -9.8/ 6 = - 1.63 m/s

If the there is negative sign it means that acceleration applied is in opposite direction .

recheck the answer