Question

Molly is driving her car at 17 m/s when she notices that the traffic light has turned orange. She brakes, causing the car to decelerate at 9 m/s² to stop in time before the traffic light turns red. How much time does it take for Molly to come to a stop?

a. 1.33 s
b. 1.89 s
c. 2.00 s
d. 2.67 s

Answer 1

Molly's car decelerates from 17 m/s to a stop at -9 m/s², taking 1.89 seconds to come to a complete stop, which is answer (b).

Step-by-step explanation:

To find out how much time it takes for Molly to come to a stop, we can use the formula for uniform acceleration, which is v = u + at, where v is the final velocity, u is the initial velocity, a is the acceleration (or deceleration in this case), and t is the time. Since Molly is coming to a stop, her final velocity v will be 0 m/s. Also, we know her initial velocity u is 17 m/s and the deceleration a is -9 m/s² (negative because it's deceleration).

Plugging in the values, we get: 0 = 17 - 9t, which we can rearrange to find t: 9t = 17, hence t = 17/9. Calculating this gives us approximately 1.89 s. Therefore, the correct answer is (b) 1.89 s.