In U.S. football, after a touchdown the team has the opportunity to earn one mor

Question

In U.S. football, after a touchdown the team has the opportunity to earn one more point by kicking the ball over the bar between the goal posts. The bar is 10.0 ft above the ground, and the ball is kicked from ground level, 36.0 ft horizontally from the bar (the figure (Figure Football regulations are stated in English units, but convert to Sl units for this problem. There is a minimum angle above the ground such that if the ball is launched below this angle, it can never clear the bar no matter how fast it is kicked. What is this angle? Phi= If the ball is kicked at 52 degree above the horizontal, what must its initial speed be if it to just clear the bar? C_0= m/s Express your answer in m/s vo m/s If the ball is kicked at 52 degree above the horizontal, what must its initial speed be if it to just clear the bar? Express your answer in km/h. c_0= km/h

Explanation / Answer

y = 10ft = 3.048 m

x = 10.97m

a) that angle is tan (a) = 3.048/10.97

a = 15.1 degree

Initial angle should be more than a for any speed

b) for a = 52 degree

if its speed is V than vertical speed Vsin(a)

Using Newtons law in vertical direction

v2 - u2 = 2gs

s = 3.048 m ; g =9.8

{Vsin(a)}2 = 2 * 9.8* 3.048 = 59.74

V sin (a) = 7.73

V =7.73/ sin 52 = 7.73 / 0.788 = 9,8m/s to just clear the bar

c) (9.8 *18)/5 = 35.28 Km/hr

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