Answer:
(D) 36,000 W
Explanation:
mass (m) = 900 kg
initial velocity (u) = 20 m/s
final velocity (v) = 0 m/s
time (t) = 5 s
What is the average power that the brakes produce in stopping the car?
average power =[tex]\frac{work}{time}[/tex] = [tex]\frac{force x distance}{time}[/tex] = [tex]\frac{mass x acceleration x distance}{time}[/tex]
we need to find the acceleration and the distance it took before the car stopped before we can apply the formula above.
- we can get the acceleration from v = u + at
0 = 20 + (a x 5)
-20 = 5t
t = -4 m/s^{2} ( the negative sign shows the car is decelerating)
- we can get the distance from ut + [tex]0.5at^{2}[/tex]
= (20 x 5) + ([tex]0.5 x (-4) x 5^{2}[/tex])
= 100 - 50 = 50 m
now that we have found the acceleration and distance we can apply the formula for the average power
= [tex]\frac{900 x 4 x 50}{5}[/tex] = 36,000 W
