Question

Starting from rest a car acquires a velocity of 30km/h in 10 s and then brakes are applied ,it take 20s to stop.Calculate the distance travelled by the car. *​

Answer 1

Question:-

Starting from rest a car acquires a velocity of 30km/h in 10 s and then brakes are applied ,it take 20s to stop.Calculate the distance travelled by the car.

Given:-

• The car starts from rest
• The final velocity of the car is 30km/h[u = 30km/h].
• Then the brake I applied [ v = 0 ].
• Time taken by the car to come to rest is 20 seconds.

To Find:-

• Calculate the distance travelled by the car.

Formulas:-

• v = u + at
• v² - u² = 2as
• s = ut + 1/2 at²

Solution:-

u = 0 ; t = 10sec ; v = 8.333m/s ; a = ? ; s = ?

First , we have to find the acceleration.

a = v - u

t

a = (8.333 - 0)/10

a = 0.8333m/s²

Now, we have to find the distance.

s = ut + 1/2 at²

s = 1/2 × 0.8333 × 10 × 10

s = 0.8333 × 10 × 5

s = 41.665 ......(1)

Now,

u = 8.333m/s ; v = 0 ; t = 20sec ; s = ? ; a = ?

a = (v - u)/t

a = (0 - 8.333)/20

a = -8.333/20

a = -0.41665 m/s²

Now, s = ?

s = ut + 1/2 at²

s = 8.333(20) + 1/2 × -0.41665 × 20 × 20

s = 166.66 + ( -0.41665 × 20 × 10 )

s = 83.33 ....(2)

Now,

Total distance covered by the car is S1 + S2

= 41.665 + 83.33

= 124.995m