Question

Q A car is traveling at 72 km/hr. Brakes are applied and the
car reduces its speed to 36 km/hr after a distance of 10 m.
Find the retardation of the car.​

Answer 1

Given :

Initial velocity = 72km/hr

Final velocity = 36km/hr

Distance travelled = 10m

To Find :

Retardation of the car.

Solution :

■ Acceleration is defined as the rate of change of velocity.

• It is a vector quantity having both magnitude as well as direction.
• It can be positive, negative or zero$.$
• SI unit : m/s²

Car is moving with constant acceleration so we can easily apply equation of kinematics to solve this problem.

First of all we need to convert km/hr into m/s.

We know that, 1 km/hr = 5/18 m/s

1. Initial velocity :

• 72km/hr = 72 × 5/18 = 20m/s

2. Final velocity :

• 36km/hr = 36 × 5/18 = 10m/s

✵ Third equation of kinematics is given by

➠ v² - u² = 2as

• v denotes final velocity
• u denotes initial velocity
• a denotes acceleration
• s denotes distance

By substituting the given values;

➠ 10² - 20² = 2a(10)

➠ 100 - 400 = 20a

➠ -300 = 20a

➠ a = -30/2

➠ a = -15 m/s²

[Note : Negative sign shows retardation]

Answer 2

Explanation:

here is the answer -15m/s