Physics question

Question

A place-kicker must kick a football from a point 36.0 m (about 40 yards) from the goal. Half the crowd hopes the ball will clear the crossbar, which is 3.05 m high. When kicked, the ball leaves the ground with a speed of 23.2 m/s at an angle of 49.0° to the horizontal.

(a) By how much does the ball clear or fall short (vertically) of clearing the crossbar? (Enter a negative answer if it falls short.)

Answer 1

Hasmik

Initial horizontal speed (constant) = 23.2 cos 49°

It will take 36 / (23.2 cos 49°) seconds for the ball to cross the goal line

s = ut + 0.5 a t². s = vertical height (0 being the ground), u = 23.2 sin 49°°, a = -9.81 m/s/s

t = 36 / (23.2 cos 49°)

s = 36 tan 49° - 0.5 x 9.81 x (36/23.2 cos 49°)^2 = 14 m

So the ball will clear the crossbar by 14 - 3.05 = 10.95 m

Mike.