Friday
May 24, 2013

# Homework Help: physics

Posted by Abdela said yimer on Saturday, January 28, 2012 at 7:11am.

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?

• physics - drwls, Saturday, January 28, 2012 at 7:44am

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.

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