4) A soccer
player
takes a penalty kick towards the goal. The angle at which the ball
leaves
his/her
boot is 53 with respect to the ground. The penalty spot is 30 ft from
the
goal and the
cross
bar is 8 ft high (g = 32 ft/s2, tan(53) = 4/3).
(a) If the ball hits the cross
bar (i.e. it is exactly 8 ft high after traveling 30 ft), how long does
it
take
to reach the bar ? (9)
Eliminating
vi between these equations leaves,
(b) What must be the initial velocity of the ball, vi ? (6)
Given t then,
(c) Determine the
horizontal
and vertical components of the velocity of the ball upon impact
with
the cross bar. (6)
x component is unchanged,
y
component is given by,
(d) Sketch these velocity
components and determine the tangent of the angle the velocity
vector
makes with the vertical at the cross bar. (4)