A car is traveling with a constant speed when the driver suddenly applies the brakes, giving the car a deceleration of 3.50 m/s². If the car comes to a stop in a distance of 30.0 m, what was the car's original speed? A) 10.2 m/s B) 14.5 m/s C) 105 m/s D) 210 m/s E) 315 m/s

Question

Quizplus · Accepted Answer

We can use the kinematic equation:

v^2 = u^2 + 2as

where v=0 (final velocity), u is the initial velocity, a is the acceleration (which is -3.50 m/s^2 here, since it is a deceleration), and s is the displacement (which is 30.0 m here).

Plugging in the values, we get:

0 = u^2 + 2(-3.50)(30.0)

Simplifying, we get:

u^2 = 210

Taking the square root of both sides (note that we ignore the negative solution since the speed must be positive), we get:

u = 14.5 m/s

Therefore, the car's original speed was 14.5 m/s. Answer choice B is correct.

A Car Is Traveling with a Constant Speed When the Driver