Next, Walter Lewin shoots the golf ball while his device makes an angle
θ with the horizontal.
For that case one has
v0x
= v0 cos(θ)
and
v0y
= v0 sin(θ)
Walter Lewin wants to predict
at which distance d
from his shooting device the golf ball hits the ground.
This can be done with
y(t)
= v0yt
- gt2/2
= t ( v0y
- gt/2 )
= t (
v0 sin(θ)
- gt/2 )
That expression equals zero (when the ball is at the ground) for
t1 = 0
and for
t2
= 2v0 sin(θ) / g
The former solution,
t1,
agrees with the instant that the ball is launched,
the latter,
t2,
with the instant that the ball returns to the ground.
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