Dini is riding her bike eastward at a constant 9.5 m/s when a car pulls out of a side street a short distance in front of her. Dini applies her brakes and manages to stop in 2.5 s, just in time to avoid running into the car. Calculate Dini's average acceleration.
The answer is -3.8 m/s^2 [E], but my teacher said that the final answer is 3.8 m/s^2 [W]. Why is it west when she's still going in the same direction, but just slowing down?
To calculate Dini's average acceleration, we can use the following formula:
Average acceleration = (final velocity - initial velocity) / time
In this case, Dini's initial velocity is 9.5 m/s (eastward) and she comes to a stop, so her final velocity is 0 m/s. The time taken to stop is given as 2.5 seconds.
Using the formula, let's calculate the average acceleration:
Average acceleration = (0 m/s - 9.5 m/s) / 2.5 s
Average acceleration = -9.5 m/s / 2.5 s
Average acceleration = - 3.8 m/s^2
The negative sign indicates that the acceleration is in the opposite direction to Dini's initial motion, which is eastward. So, the average acceleration is -3.8 m/s^2, eastward.
It seems there might have been a misunderstanding between you and your teacher regarding the direction. When Dini applies her brakes and comes to a stop, she is indeed slowing down, but her acceleration is still in the opposite direction to her motion, which is eastward. Therefore, the correct answer should be -3.8 m/s^2, eastward.