Deceleration Formula
Deceleration is the opposite of acceleration. It is the rate at which an object slows down. Deceleration is the final velocity minus the initial velocity, with a negative sign in the result because the velocity is dropping. The formula for acceleration can be used, recognizing that the final result must have a negative sign.
deceleration = (final velocity - initial velocity) / time
d = (vf - vi)/t
d = deceleration
vf = final velocity
vi = initial velocity
t = time
Deceleration Formula Questions:
1) You are driving at 100 m/s and a cat runs out in front of your car. You stop rapidly, which takes 5 seconds, and miss the cat. What is your deceleration?
Answer: The initial velocity, vi = 100 m/s. The final velocity, vf = 0 m/s. The time, t = 5 sec.
d = (vf - vi) /t
d = (0 m/s - 100 m/s)/ 5 sec
d = -100m/s / 5 sec
d = - 20 m/s2
2) You and a friend are driving on the highway at 150 km/hr when you see a police car ahead. You decelerate to 120 km/hr, which takes you 2 seconds. What is your deceleration in km/sec?
Answer:
The initial velocity, vi = 150 km/hr x 1/3600 hr/sec = 0.042 km/sec. The final velocity, vf = 120 km/hr x 1/3600 hr/sec = 0.033 km/sec. The time, t = 2 sec.
d = (vf - vi) /t
d = (0.033 km/sec - 0.042 km/sec) / 2 sec
d = - 0.009 km/sec / 2 sec
d = - 0.0045 km/sec2
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