As an aid in working this problem, consult Interactive Solution 3.41. A soccer player kicks the ball toward a goal that is 25.0 m in front of him. The ball leaves his foot at a speed of 16.2 m/s and an angle of 38.0 ° above the ground. Find the speed of the ball when the goalie catches it in front of the net.

Respuesta :

Answer:

15.77m/s

Explanation:

the information we have is:

initial velocity [tex]v_{0}=16.2m/s[/tex]

distance: [tex]d=25m[/tex]

angle: [tex]\theta=38[/tex]°

first we need to break down the velocity into its x and y components:

initial velocity in x (the velocity in x is constant):

[tex]v_{0x}=v_{0}cos\theta\\v_{0x}=(16.2m/s)cos38\\v_{0x}=12.766m/s[/tex]

and initial velocity in y (the velocity in y is not constant due to acceleration of gravity):

[tex]v_{0y}=v_{0}sin\theta\\v_{0y}=(16.2m/s)sin38\\v_{0y}=9.97m/s[/tex]

and now we find the time that the ball was in the air:

[tex]t=\frac{d}{v_{0x}} =\frac{25m}{12.766m/s}\\ t=1.96s[/tex]

and with this time, we find the y component of the volicity at time 1.96s:

[tex]v_{y}=v_{0y}-gt\\v_{y}=(9.97m/s)-(9.81m/s^2)(1.96s)\\v_{y}=-9.26m/s[/tex](negative because it points downward)

finally, to find the final velocity we use pythagoras:

[tex]v_{f}=\sqrt{v_{x}^2+v_{y}^2} =\sqrt{12.766^2+(-9.26)^2}=15.77m/s[/tex]