Question

Homework #5 Problem 3.36 Part A A soccer player takes a free kick from a spot that is 17 m from the goal. The ball leaves his foot at an angle of 35°, and it eventually hits the crossbar of the goal, which is 2.4 m from the ground. At what speed did the ball leave his foot? Express your answer with the appropriate units. 이 ? 17.26 Submit Previous Answers Request Answer X Incorrect; Try Again; 4 attempts remaining Provide Feedback

Answer 1

$\\along \;vertical\\\\ initial \;velocity \;v_{oy} = v_i\;sin\theta\\\\ acceleration \;a_y = -g = -9.8 m/s^2\\\\ initial \;position \;y_o = 0\\\\ final \;position \;,y = 2.4\;m\;\\ from \;equation \;of \;motion\\\\ y-y_o = v_{oy}\;T + \frac{1}{2}\;a_y*T^2 ------(2)\\\\ using(1)in(2)\\\\ y-y_o = (x-xo)\;tan\theta\;-\frac{1}{2}\;g\;\frac{(x-x_o)^2}{v_i^2\;cos^2\theta}\\\\ 2.4 - 0 = (17-0)(tan35)-\frac{0.5*9.8*(17-0)^2}{(vi^2*(cos35)^2)}\\\\\\ v_i=15\;m/s$