Finding x and y components of velocity?

[santoki]

Question:

A soccer player kicks the ball off the ground at an angle Θ above the horizontal. The ball is in the air for 3.0 seconds and lands 40 m away (assume the field is level).

a) Make a table of x and y components and fill out what you know, based on the problem statement above, and your knowledge of kinematics (don’t calculate anything yet). Draw a box around your table.
b) Now work outside of the box. Find the soccer ball’s initial horizontal (vox) velocity component.
c) Find the soccer ball’s initial vertical (voy) velocity component.

Attempt:

a)
x-component

• d = 40m
• t = 3s
• v_o = 0m/s
• a = 0m/s²

y-component

• a = 9.8m/s²
• t = 3s
• v = 0m/s

b)
d = vt
40 = 3v
v = 13.3m/s

c)
v = v_o - gt
v = 0 - (9.8)(3)
v = -29.4m/s

am I on the right track or am I supposed to find that missing angle?

 

[NascentOxygen]

Time t=0 starts the moment that the ball loses contact with the player's boot. So neither of the $V_0$ terms is zero.

 

[BruceW]

yeah. I agree with Nascent. In this kind of situation, you're only concerned with the motion of the ball immediately after it has been kicked. That is why you are able to say a=0 for the horizontal acceleration. You have used this fact for part b) since the formula d=vt assumes zero acceleration. p.s. you have the right answer for part b)

For part c), it's not quite right. Remember you are supposed to find the initial vertical velocity (immediately after the ball has left the player's boot, so it's not going to be zero). Also, you don't need to find the missing angle, but you could do it that way if it makes more sense to you.