SPH4UI Lecture 1 Notes - The Burns Home Page

“x” and “y” components of motion are independent.
• A man on a train tosses a ball straight up in the air.
‣View this from two reference frames:
Reference frame
on the moving train.
Problem:
• David Eckstein clobbers a fastball toward center-field. The
ball is hit 1 m (y o ) above the plate, and its initial velocity is
36.5 m/s (v ) at an angle of 30 o () above horizontal. The
center-field wall is 113 m (D) from the plate and is 3 m (h)
high.
• What time does the ball reach the fence?
• Does David get a home run?
Reference frame
on the ground.
y 0
v
h
D
• Choose y axis up.
Problem...
Problem...
• Use geometry to figure out v 0x and v 0y :
g
y
v
v x = v 0x v y = v 0y - gt
y 0
x = v x t y = y 0 + v 0y t - 1 / 2 gt 2
• Choose x axis along the ground in the direction of the hit.
• Choose the origin (0,0) to be at the plate.
• Say that the ball is hit at t = 0, x(0) = x 0 = 0. y(0) = y 0 = 1m
• Equations of motion are:
Find v 0x = |v| cos .
and v 0y = |v| sin .
v 0y
v 0x
remember, we were told that = 30 deg
x
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