Question

The speed time graph of a car of 1000kg mass is given . On the basis of this, answer the following question.

Answer 1

Given , mass of the car (m) = 1000 kg  

(i) As, shown in graph,

Distance covered in first 2 sec  

= Area of  Δ inscribed in first 2 s.

= 1 / 2 × base × height  

= 1 / 2 × 2 ×15 = 15 m  

(ii) Force (F) = mass (m) × acceleration (a)

Time taken by force to stop car = 6 - 5 = 1

second  

Initial velocity (i.e. velocity at B) = 15 m/s

Final velocity (at point C) = 0 m/s  

using equation v = u + at  

a = (v-u) / t = (0 -20) / 0.02 = -15 m/s2

(-ve sign indicates that it is retardation )

Force applied by brakes = 1000 × -15 = -15000 N  

= - 15 KN