Finding maximum Height

[pennywise1234]

Homework Statement

A soccer ball is kicked at a 45° angle. If the ball is in the air for 3 s, what is the maximum height achieved

Homework Equations

y=viy + 0.5 x ay x t

The Attempt at a Solution

i used trig to get the vertical and horizontal components i got 2.2 for each side (as there the same with a 45 degree angle)

i used y=0 + 0.5 x (-9.81) x (3s)

is this right ^^

 

[rpthomps]

your equation is not correct.

 

[pennywise1234]

i used y=0 + 0.5 x (-9.81) x (1.5s)Square root

is what i meant to put

 

[rpthomps]

I think you mean squared, not square root.

 

[pennywise1234]

yes, sorry

 

[haruspex]

i got 2.2 for each side

You got 2.2 what? You don't know the velocity, so how can you get the velocity components?
What does your y₀ represent?

 

[pennywise1234]

y=o represents initial velocity. but it is not known like you said, so that is how i was able to get 11.05 but setting initial to 0

 

[rpthomps]

The initial velocity cannot be 0. Otherwise, with gravity being the only accelerator the projectile would go down.

 

[rpthomps]

It's possible to calculate your initial velocity though, assuming the projectile lands on level ground. Can you modify your relationship above to help you find this?

 

[haruspex]

y=o represents initial velocity. but it is not known like you said, so that is how i was able to get 11.05 but setting initial to 0

Setting it zero will get you nowhere. Create an unknown for it, v.
Your equation for y is suitable for a vertical displacement, not a vertical velocity. In terms of v, what would the vertical displacement be at time t? What is the vertical displacement when it lands?

 

[pennywise1234]

I am trying to find displacement though

 

[haruspex]

I am trying to find displacement though

You are asked to find, eventually, the vertical displacement from launch to the highest point. I asked you what the vertical displacement is from launch to where it lands.