Finding speed

staceyrho

Junior Member
Joined
Jan 12, 2007
Messages
76
A man can throw a ball a maximum horizontal distance of 184m.
the acceleration of gravity is 9.8 m/s^2. How far can he throw the same ball vertically upward with the same initial speed?
Answer in units of m.

Does anyone know what formula will solve this?
 
this is the horizontal "range" equation ...

\(\displaystyle \L \Delta x = \frac{v_o^2 \sin{(2\theta)}}{g}\)

... do you know what angle \(\displaystyle \L \theta\) maximizes the range?
 
Hello, Stacey!

That can't be the original wording of the problem . . .


A man can throw a ball a maximum horizontal distance of 184m.
The acceleration of gravity is 9.8 m/s².
How far can he throw the same ball vertically upward with the same initial speed?
Answer in units of m.

We need a lot more information . . .

Is he throwing the ball horizontally
. . or at some angle of elevation \(\displaystyle \theta\) ?
If it's thrown at an angle, you're expected to know that
. . maximum horizontal distance occurs when \(\displaystyle \theta\.=\,45^o\).
(Too bad if you didn't know that!)

Is he throwing it from ground level
. . or is he releasing the ball at some point above his head?

 
soroban said:

That can't be the original wording of the problem . . .


A man can throw a ball a maximum horizontal distance of 184m.
The acceleration of gravity is 9.8 m/s².
How far can he throw the same ball vertically upward with the same initial speed?
Answer in units of m.

We need a lot more information . . .


actually, it can be the original wording of the problem.

in a first year physics class, students start with problems involving projectiles moving in one dimension ... up and down.

they then progress to motion in two dimensions, most commonly covering what are called "horizontal shots" from some initial height, and then "ground to ground" shots, where the formula given in my previous post is derived and discussed with regard to launching from different angles ... a good instructor usually has his students graph range vs. launch angle using this formula so they may "discover" the optimum launch angle among other interesting details.

so ... IMHO, this problem is designed to have students find the initial speed that the projectile is launched that will result in the given horizontal displacement, with the condition that this displacement is a maximum. once they find this initial speed, they revert back to the one-dimensional problem of finding a maximum height for a certain speed.
 
yeah stupidly enough that is the entire question. I have struggled with trying to figure this one out.
 
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