# College Physics Problem 2.18

#### A commuter backs her car out of her garage with an acceleration of $1.40\:m/s^{2}$ . (a) How long does it take her to reach a speed of 2.00 m/s? (b) If she then brakes to a stop in 0.800 s, what is her deceleration?

SOLUTION:

a) The formula for acceleration is

$a=\frac{v_f-v_0}{t}$

If we rearrange the formula by solving for the t, in terms of velocity and acceleration, we come up with

$t=\frac{v_f-v_0}{a}$

$t=\frac{2.00\:m/s-0\:m/s}{1.40\:m/s^{2}}$

$t=1.43\:s$

b) The formula for acceleration (deceleration) is

$a=\frac{v_f-v_0}{t}$

$a=\frac{0\:m/s-2\:m/s}{0.8\:m/s^{2}}$

$a=-2.50\:m/s^{2}$

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