If the engine of a car provides an acceleration of 2m/s^2 to start it from rest, assuming the mass to be roughly 1000kg,calculate time after which car the comes to rest , if the engine is turned off after 15 seconds.(Frictional Force = 15N)
the velocity of car after 15s will be
v = u + at
here,
u = 0
a = 2 m/s2
t =15s
so,
v = 0 + 2x15 =30 m/s
now, after the engine is turned off
the deceleration caused will be
a = F/m
[from F = ma]
here,
F = 15N (frictional force)
m = 1000kg
so,
a = 15/1000 = 0.015 m/s2
now,
the time taken to completely stop
t = (v - u) / a
here,
v = 0 m/s
u = 30 m/s
so,
t = (0 - 30) / -0.015
thus,
t = 2000s