# physics question need help

Discussion in 'Homework Help' started by zelda1850, Jan 3, 2010.

1. ### zelda1850 Thread Starter New Member

Jan 3, 2010
18
0
A kicked soccer ball has an initial velocity of 25 meters per second at an angle of 40 degrees above the horizontal level ground [neglect friction]

A)calculate the magnitude of the vertical component of the balls initial velocity

b) calculate the maximum height of the ball reaches above its initial speed

c) sketch the balls height from the its initial position at point p until it returns to level ground

i understand how to do the first question but how can i figure out the maximum height for b?

Jul 3, 2008
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3. ### zelda1850 Thread Starter New Member

Jan 3, 2010
18
0
emm heres my attempt

A) Viy sin 40 degrees

B) dy= vytrise is this the correct equation?

c) im not sure how i can sketch it yet

im confused with the 2nd problem how can i find maximum height if somoene can explain to me that wll help alot ^-^

4. ### thyristor Active Member

Dec 27, 2009
94
0
I think you know the answer to part a), just do the calculation.

A hint for part b): What will be the ball's vertical velocity when it reaches its maximum height?

A hint for part c): What well-known shape will the ball's trajectory display? (This is basic ballistics knowledge)

Jul 7, 2009
1,585
141
The aha! moment for many basic physics students with this problem comes from them realizing the proper model of the situation. Two key points are:

1. The horizontal motion is free particle motion, as there's no horizontal force on the ball after the kick.
2. The vertical motion is a pure kinematic one and you've no doubt already been given the constant acceleration (i.e., constant force) kinematic equations for this type of motion.
The third concept needed is the ability to resolve the initial velocity vector into the relevant components.

6. ### Fraser_Integration Member

Nov 28, 2009
142
5
Just write out all of the SUVAT (distance, init velocity, end velocity, acceleration, time) values you have for vertical and horizontal motion separately, and apply the any of the following formulas.

v = u + at
s = ut + 0.5at^2
v^2 = u^2 + 2as

7. ### hitmen Active Member

Sep 21, 2008
159
0
Uy = 25 sin 40 degrees
Vy = 0
g = -9.81ms-2
This could be good enough. Just sub in values