Question

A body changes its speed from 72km/hr to 54km/hr . if the change occur in 2.5 seconds find the acceleration ​

Answer 1

Initial Speed, u = 72 km/h

Final Speed, v = 54 km/h

Time taken, t = 2.5 sec

Acceleration, a = ( v – u ) / t

a = ( 54 – 72 ) / 2.5

a = – 18 / 2.5

a = – 180 / 25

a = – 7.2 m/s²

Answer 2

Answer

• Acceleration , a = - 0.5 m/s²

Given

• A body changes its speed from 72 km/hr to 54 km/hr .  The change occur in 2.5 seconds

To Find

• Acceleration

Solution

Initial velocity , u = 72 km/h

SI units of Velocity is in m/s. So convert it into m/s.

To Convert velocity from km/h to m/s , We need to multiply with ⁵/₁₈ .

So ,

Initial velocity , u = 72 × ⁵/₁₈

⇒ Initial velocity , u = 20 m/s

Final velocity , v = 54 × ⁵/₁₈

⇒ Final velocity , v = 15 m/s

Change in velocity , Δv = v - u

⇒ Δv = 15 - 20

⇒ Δv = - 5 m/s

Time , t = 2.5 s

Now , Acceleration is defined as , " Rate of change of velocity "

⇒ a = Δv / t

⇒ a = - 5 / 2.5

⇒ a = - 2 m/s²

- ve sign denotes the retardation or deceleration