An object of mass m moving with initial speed of 15 m/s got an acceleration of 10 m/s^ after a constant force F is applied to it. How long does it take for the object to reach 90 meters from its initial position?

Answer 1

With acceleration of 10 m/s^2,and initial velocity of 15 m/s, the displacement from initial position is

X = 15 t + 5 t^2

If X = 90,
5t^2 + 15t -90 = 0
t^2 + 3t -18 = 0
(t+6)(t-3) = 0

The positive solution is t = 3 seconds. Ignore the negative solution; it is outside the domain of the function.

Answer 2

S=Ut+1/2at^2
90=15t+1/2(10)t^2
90=15t+5t^2
90/5=15t/5+5t^2/5
18=5t+t^2
(t+6)(t-3)
t=-6 t=3
So the time does not be negative so the answer is t=3