Summary Kinematics in vertical motion Gr 12 IEB & DBE notes

Kinematics
in vertical
motion

, Vertical motion
( Vf +2 Vi )
In equations of motions, a (acceleration) with g (force of gravity)
1) Vf = Vi + a▵t 2) ▵X=Vi▵t + 1/2a▵t 3) Vf = Vi + 2a▵x
2
4)▵X =
2 2



Vertical projectile
If an object which is free falling, only force acting on the object is the force of gravity (Fg),
9.8m.s-2 downwards if ignore air resistance
Normal free falling objects
Eg.1) Someone stands on balcony 20m above ground. Tosses rubber ball upwards, initial
velocity 4.9m.m-1. Ball travels up to max height the falls. Upwards is the positive direction.
1. Calculate the maximum height reached from the ground by the rubber ball
Vi: +4.9m.s-1 Vf: 0m.s-1 g: -9.8m.s-2 ▵X :? + 20m = max height
Vf^2 = Vi^2+2a▵X
O = (4.9)^2 + 2x(-9.8)X
-24.01=-19,6X
X=1.23 (+20)
Max height = 21.23m
2. Calculate time taken for rubber ball to fall to ground from its max height
Vi: 0.s-1 g: -9.8m.s-2 ▵X -21,23 t=?
▵X= Vi(t) + 1/2at^2
-21,23 = 0 + 1/2 (-9.8)t^2
t=2,08 seconds
3. With what velocity does the rubber ball hit the ground (Just before ball hits the ground)

Vi: 0.s-1 g: -9.8m.s-2 ▵X -21,23 t=2,08s Vf:?
Vf=Vi + at
Vf= 0 + (-9.8)(2.08)
Vf= -20,38 m.s-1
Vf= 20,38m.s-1 downwards