Question

a car is moving with a velocity of 80 km/h on a road on the applications of breaks its comes to rest after covering 30 metre calculate that the deceleration of the car numericals
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Answer 1

Given :

Initial velocity, u = 80km/hr.

Final velocity, v = zero.

Distance covered, s = 30m.

To find :

The deceleration of the car.

Solution :

First of all we have to convert km/hr to m/s

1km/hr = 8/15 m/s

80km/hr = 80 × 8/15 = 42.6m/s

As we are provided with initial velocity, final velocity and distance we can use 3rd equation of motion.

So, using 3rd equation of motion .i.e.,

${ \leadsto{ \bf{ v^2 - u^2 = 2as}}}$

${ \leadsto{ \sf{(0)^2 - (42.6)^2 = 2(a)(30)}}}$

${ \leadsto{ \sf{- 1814.76 = 60a}}}$

${ \leadsto{ \sf{a = - \dfrac{ 1814.76}{60 }}}}$

${ \leadsto{ \sf{ a = - 30.24 \: m/s²}}}$

|| negative sign detects declaration ||

thus, deceleration of car is 30.24 m/s²

Remember !

If the speed is decreasing with time then acceleration is negative. The negative accerlation is called retardation or deceleration.