Answer:
45 s
Explanation:
To find the time it takes to stop, we first find the deceleration, a of the car from
v² = u² + 2as and a = (v² - u²)/2s were v = final velocity of car = 0 mph = 0 m/s, u = initial velocity of car = 30 mph = 30 × 1609.34 ft ÷ 3600 s = 13.41 ft/s and s = distance = 300 ft. Substituting the values into a, we ave
a = (v² - u²)/2s = (0² - 13.41²)/2×300 = -0.3 ft/s²
We then find the time for this deceleration from v = u + at ⇒ t = (v - u)/a
t = (v - u)/a = (0 - 13.41 ft/s)/-0.3 ft/s² = - 13.41 ft/s/-0.3 ft/s² = 44.7 s ≅ 45 s
So it takes 45 seconds to stop.
