Hi, Please, can you explain step by step. Questions 8 through 13 have to do with

Question

Hi,
Please, can you explain step by step.

Questions 8 through 13 have to do with projectiles. A kicker attempts a field goal from 30 m away from the goal posts. The ball has an initial velocity of 20 m/s and an initial launch angle of 40 deg. The cross bar is 3.0 m high. Neglect air resistance If the ball is kicked at time t = 0 when will it reach the x position of the goal posts? (A) 1.5 sec. (B) 2.2 sec. (C) 1.96 sec. (D) 1.15 sec. How high will it be (y = ?) when it reaches the goal posts (if it does)? (A) 3.2 m (B) 5.2 m (C) 6,4 m (D) 8.5 m (E) 13.2 m What is the minimum initial velocity for which the ball will make it over the cross bar? (with = 40 degrees) (A) 15.4 m/s (B) 17.5 m/s (C) 20 m/s (D) 22.4 m/s (E) 18.4 ra/s

Explanation / Answer

        Q8)              Horizontal distance, X = 30 m              Initial velocity, U = 20 m/s              Angle of projection, = 40 o              Time, t = X / ( U cos )                         = 30 / ( 20 cos 40 )                         = 1.96 s ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~         (9)           Vertical displacement, Y = ?            Y = ( U sin ) t - ( 1/2 ) g t2                = 20 sin 40 * 1.96 - ( 0.5 * 9.8 * 1.96 2 )                = 6.4 m ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~        (10)           Vertical displacement, Y = 3 m            Y = X tan - [ g / ( 2 U 2 cos 2 ) ] X 2             3 = 30 tan 40 - [ 9.8 / ( 2 U 2 cos 2 40 ) ] * 302           Bysimplification, we get Velocity of projection, U = 18.4m/s

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