The velocity time graph of a car of mass 1000 kg is given
below. From the graph answer the following :
(a)When is the maximum force acting on the car? Why?
(b}What is the retarding force?
(c)For how long is there no force acting?
Answers
(a) The maximum acts on the car when it is at a velocity of 15m/s and time is 4 seconds. This is because force is equal to mass * acceleration. Thus from 0sec (rest position) till 4sec, from a velocity of 0m/s to 15m/s, the acceleration is greatest. Since mass is constant, thus, the maximum force acting on the car is when it is at a velocity of 15m/s at 4sec.
(b) Time (t) = 12 seconds - 10 seconds
=> Time (t)= 2 seconds
Initial velocity (u) = 15m/s
Final velocity (v) = 0m/s (rest)
Thus, acceleration (a)
= (0 - 15)/2 m/s²
= (-7.5)m/s²
Mass (m) = 1000 kg
Thus, force (F)
= {(-7.5) * 1000}kgm/s²
= (-7500)N
The minus sign indicates that it is a retarding force.
Thus, the retarding force acting on the car is 7500N.
(c) From point A to point B no force is acting on the car. This is because there is no change in velocity from time 4 seconds to 10 seconds. Thus, the force that started acting on the car at 4th second remains constant till 10th second and after that force started acting on the car.
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