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

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