Question

A car moving with velocity 54 km/h travelling on a straight road on applying brakes stops after covering 20 m. Find acceleration of the car

Answer 1

Step 1: Given

Initial velocity of car, (u) = 54 km/h = $54\times \frac{5}{18}=15$ m/s
Distance travelled by car before stopping (S) = 20 m

The final velocity of the car (v) = 0 m/s

a is acceleration, S is the distance covered.

Step 2: Formula used

$v^2=u^2+2as$

Where; v = Final velocity , u = initial velocity, a= acceleration and s = distance covered by the body

Step 3: Finding the acceleration

Putting all the values
⇒ 0 = (15)² + 2 × a × 20
⇒ -225 = 40×a
⇒ a = -5.625 m/s²

[Here negative sign shows that acceleration is the opposite direction of motion of the car. That is it is retardation. ]

Hence, the acceleration of the car is 5.625 m/s².