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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
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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.
