# AP Physics B: Kinematics and Free Fall Free Fall problems include situations where the acceleration is due to gravity (only)

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AP Physics B: Kinematics and Free Fall Free Fall problems include situations where the acceleration is due to gravity (only)

Free Fall Ideas g = acceleration due to gravity g = 9.8 m/s/s but you are welcome (and encouraged) to use g= 10.0 m/s/s Using g = 10.0 m/s/s allows you to easily solve problems in your head. Also, the AP test allows you to use g = 10.0 m/s/s

Free Fall Solving Free Fall problems: Draw a picture whenever possible Choose a direction for “positive”. If an object is initially thrown upwards I make the upwards direction positive. In this case g = - 10.0 m/s/s If an object is dropped from rest or thrown downwards, I typically make downwards the positive direction. In this case g = + 10.0 m/s/s Whatever direction you call positive, providing you are consistent with the sign convention in that problem, you’ll be fine.

Free Fall If an object is thrown upwards and then falls back down, sometimes its best to break the problem into two parts. First solve for the “upwards” part until the object reaches a zero velocity at the peak of its motion Then solve for the falling part. Example: A ball is thrown upwards at 30 m/s. What is the total distance traveled in 4 seconds? It takes 3 seconds to go up, so time (up) = 3 sec. The distance to go up is d = ½ a t*t = 45m. Then it falls for 1 sec so using d = ½ a t*t again it falls a distance of 5m. The total distance traveled is 50 m, the total displacement from the origin is 40m.

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