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# A Car is Travelling at 20 M/S Along a Road. a Child Runs Out into the Road 50 M Ahead and the Car Driver Steps on the Brake Pedal. What Must the Car’S Deceleration - CBSE Class 9 - Science

ConceptGraphical Representation of Motion - Distance-time Graphs

#### Question

A car is travelling at 20 m/s along a road. A child runs out into the road 50 m ahead and the car driver steps on the brake pedal. What must the car’s deceleration be if the car is to stop just before it reaches the child ?

#### Solution

We have to find the deceleration. We have the following information given,
Initial velocity, (u) = 20 m/s
Final velocity, (v) = 0 m/s
Distance travelled, (s) = 50 m
Let the deceleration for the entire journey be (a)
We can calculate acceleration by using the 3rd equation of motion,
a = (v^2-u^2)/(2s)
(s) - Displacement
(u) - Initial velocity
(a) - Acceleration
(v) - Final velocity
Put the values in above equation to find the deceleration,
a = [(0-400)/(2(50)]] "m/s"^2
= (-400/100)  "m/s"^2
= -4 "m/s"^2
Hence, deceleration is 4 m/s2.

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Solution A Car is Travelling at 20 M/S Along a Road. a Child Runs Out into the Road 50 M Ahead and the Car Driver Steps on the Brake Pedal. What Must the Car’S Deceleration Concept: Graphical Representation of Motion - Distance-time Graphs.
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