Question

(iv) The speed time graph of a car is given. The car weighs 1000 kg.
20
15
Speed (m/s)
10-
im
0 1 2 3 4 5 6
Time-
The braking force applied at the end of 5 s to bring the car to stop within 1s is.
a)-12000N
b) - 15000N
c) -16000N d) -18000N
​

Answer 1

Answer:

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