The brakes of a car are applied to give it an acceleration of -3m/s^2. The car comes to a stop in 5 s. What was its speed when the brakes were applied?
v = Vi + a t
0 = Vi - 3(5)
Vi = 15
To find the initial speed of the car when the brakes were applied, we can use the following equation:
v = u + at
where v is the final velocity (in this case, 0 m/s since the car comes to a stop), u is the initial velocity (what we're trying to find), a is the acceleration, and t is the time taken for the car to stop.
Rearranging the equation, we have:
u = v - at
Substituting the given values, we have:
u = 0 - (-3 m/s^2) * 5 s
Simplifying:
u = 0 + 15 m/s
Therefore, the initial speed of the car when the brakes were applied was 15 m/s.