A Projectile Launcher (baseball hit at a 45 degree angle to the horizontal)

[Veronica_Oles]

Homework Statement

[/B]
A baseball player hits a ball 200.0m home run. The ball travels at angle of 45° with the horizontal just after being hit. Determine the initial speed. Assume the ball lands the same height it was hit.

2. Homework Equations

The Attempt at a Solution

I am not sure how to go about this question. I think range is 200m and I know acceleration is 9.8m/s²[down] but that's about it.

 

[gneill]

You must be able to find some relevant equations. Check your course text and notes for equations related to projectile motion.

 

[Brianna I]

Ok, when I was initially taught this I was told to make a chart in both the x and y with what you know and do not know.
The setup would be something like this:
______ X _____ Y
a =
vi =
d =
t =
From there try to solve for maybe t using the y-variables (since you don't have that either) and then plugging in t in an equation that will give you V_ix.

 

[Veronica_Oles]

Ok, when I was initially taught this I was told to make a chart in both the x and y with what you know and do not know.
The setup would be something like this:
______ X _____ Y
a =
vi =
d =
t =
From there try to solve for maybe t using the y-variables (since you don't have that either) and then plugging in t in an equation that will give you V_ix.

Yes, I did this.

 

[gneill]

You need to show what you've done before we can help.

 

[Veronica_Oles]

You need to show what you've done before we can help.

I have not gotten any of it done because I have no idea which formula to use. All I know is that on my horizontal I have d = 200 m and a = 0. Then for my vertical I have d = 0 and a = 9.8m/s^2(down). I don't have time and all the formulas I was given deal with time which is why I am confused

 

[haruspex]

I have not gotten any of it done because I have no idea which formula to use. All I know is that on my horizontal I have d = 200 m and a = 0. Then for my vertical I have d = 0 and a = 9.8m/s^2(down). I don't have time and all the formulas I was given deal with time which is why I am confused

For motion under constant acceleration, there are five standard variables (usually known as SUVAT, s for displacement, u for initial speed, v for final speed, a for acceleration, t for time). There are correspondingly five equations. Each equation omits one of the five variables. Are you familiar with these?

 

[Veronica_Oles]

For motion under constant acceleration, there are five standard variables (usually known as SUVAT, s for displacement, u for initial speed, v for final speed, a for acceleration, t for time). There are correspondingly five equations. Each equation omits one of the five variables. Are you familiar with these?

Yes I know those.

 

[haruspex]

Yes I know those.

Since you do not care about time, pick one that does not involve time.

 

[Veronica_Oles]

Since you do not care about time, pick one that does not involve time.

Since you do not care about time, pick one that does not involve time.

The only one I see that doesn't involve time is vf^2 = vi^2 + 2ad

 

[haruspex]

The only one I see that doesn't involve time is vf^2 = vi^2 + 2ad

Sorry, I wasn't thinking clearly. You do care about time, but you have to start with the horizontal direction. If it is hit with speed v, how long to reach ythat distance?

 

[Veronica_Oles]

Sorry, I wasn't thinking clearly. You do care about time, but you have to start with the horizontal direction. If it is hit with speed v, how long to reach ythat distance?

T= 200/ViCos 45 ??!

 

[haruspex]

T= 200/ViCos 45 ??!

Yes.

 

[Simon Dobbs]

still confusing me

 

[haruspex]

still confusing me

What is the initial vertical speed? How long before it lands?

 

[Apashanka]

A baseball player hits a ball 200.0m home run. The ball travels at angle of 45° with the horizontal just after being hit. Determine the initial speed. Assume the ball lands the same height it was hit.

if u is the initial velocity at an angle θ with the horizontal
horizontal distance covered in time t ucosθt=R(range)...(1)
for time t/2 , vertical motion leads to usinθ=gt/2 ,hence t becomes 2usinθ/g
Putting t in (1) leads to
u²sin2θ/g=R
from which u can be determined ,θ and R is given