Question

You are driving at a speed of 30 m/s and slam on the brakes, causing an acceleration of -7.8 m/s^2. How much time does it take you to stop?"

A) 2.56 seconds
B) 3.85 seconds
C) 4.62 seconds
D) 6.25 seconds

Answer 1

Using kinematic equations, it is calculated that the car takes 3.85 seconds to stop after braking with an acceleration of -7.8 m/s^2, making option B the correct answer.

Step-by-step explanation:

To calculate the time it takes for the car to stop, we can use the kinematic equation that relates initial velocity, final velocity, acceleration, and time:
Final velocity (v) = Initial velocity (u) + Acceleration (a) x Time (t)

Since the car is coming to a stop, final velocity (v) will be 0 m/s. Plugging in the initial velocity of 30 m/s and the acceleration of -7.8 m/s2, the equation becomes:

0 m/s = 30 m/s + (-7.8 m/s2) x t

To find the stopping time (t), solve for t:

t = (0 m/s - 30 m/s) / -7.8 m/s2 = 30 m/s / 7.8 m/s2 = 3.85 seconds

Therefore, it takes 3.85 seconds for the car to stop, which corresponds to option B.