# How to get initial and final velocity? thanks

jamesblim168

## Homework Statement

a human cannonball in 1940 soared over three ferris wheels, each 18 meters high covering a horizontal distance of 10.63 meters. Assuming that the point of projection is 2.50 meters above the ground and that he landed safely on a net placed at the same level, find his initial velocity. Assuming that he missed the net and landed on the ground, with what velocity will he strike the ground?

## The Attempt at a Solution

jamesblim168
up for today...

jamesblim168
up for today...

voko
If no more conditions are given, it seems that the problem requires that you find an optimal setup for the stunt, optimal in the sense that the initial velocity is minimal.

jamesblim168
If no more conditions are given, it seems that the problem requires that you find an optimal setup for the stunt, optimal in the sense that the initial velocity is minimal.

i don't understand how... can you teach me how?

Homework Helper
You have made no attempt at all, not even citing equations that might be relevant. Are you saying that you are taking a course in which this was given as an exercise and have learned nothing about this?

voko
i don't understand how... can you teach me how?

Imagine it is you who will be fired from a cannon in order to fly over three ferris wheels. You are in full control of the arrangement. How would you approach the problem?

jamesblim168
1. Homework Statement
a human cannonball in 1940 soared over three ferris wheels, each 18 meters high covering a horizontal distance of 10.63 meters. Assuming that the point of projection is 2.50 meters above the ground and that he landed safely on a net placed at the same level, find his initial velocity. Assuming that he missed the net and landed on the ground, with what velocity will he strike the ground?

2. Homework Equations
my problem i don't know what equation il use... coz there so many missing values
is the initial velocity is 0?

3. The Attempt at a Solution
this is what i did, i know its not right i hjope you guys could help me out...
“Y=Viy * t + 0.5 * Ay * t^2 “ to solve for time
-20.50m = (0 m/s) * t + 0.5 (-9.8 m/s/s) * t^2
-20.50m = (-4.9 m/s/s) * t^2
4.1s^2 = t^2
(TIME) T= 2.02s

Problem 1:Initial velocity is 0

Problem 2: Assuming that he missed the net and landed on the ground, with what velocity will he strike the ground?

V= distance/time
V=10.63/2.02s
V=5.26m/s

jamesblim168
up for today...

jamesblim168
up for today...

azizlwl
It depends on the horizontal distance of the cannon and the first wheel, and the last wheel with the safety net.

jamesblim168
how would i know? those are the only values i have... does this mean this problem cannot be solve?

Jakeus314
An initial velocity of zero makes no sense. He wouldn't go anywhere. Can you decide where he might have to be at some point in space? Like as he approaches the first wheel?

Jakeus314
how would i know? those are the only values i have... does this mean this problem cannot be solve?

You may need to make an assumption about the placement of the first Ferris wheel and its distance from the cannon.

jamesblim168
what do you mean? how to decide?

jamesblim168
can anyone help me solve this?

jamesblim168
would really appreciate the effort ... thanks

Jakeus314
Is a drawing included? The orientation and position of the wheels will be important. If no drawing is included you will need to start the problem making an assumption about where the wheels are.

azizlwl
You can find the velocity for maximum range, the distance between the wheels.
For maximum range the angle at above first wheel is 45°.

jamesblim168
up for today...

Jakeus314
What is "up for today.." ?

azizlwl
up for today...

Can you find the velocity just above the first wheel?

jamesblim168
Can you find the velocity just above the first wheel?

no, coz i don't know how... Homework Helper
Read about "projectile motion". The man moves both in horizontal and vertical direction. There is an equation for the x and y coordinates of the trajectory.
The projectile has to fly over the three ferris wheels, 18 m high and with distance 10.63 m between the first and last ones. The man had to be at least 18 m high above the ground at the place both of the first and last wheels.
Make a drawing to show the launch place, the wheels and the trajectory of the human cannonball.
You certainly learned that you get the maximum distance if you launch a projectile at 45 degrees. The human projectile certainly used that launch angle.

ehild

#### Attachments

• cannonball.JPG
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jamesblim168
so what is my initial veloctiy if my angle is 45 degress?

Homework Helper
You have to find out both the initial velocity and the distance of launch place from the first wheel.
I attached a figure to my previous post, look at it.

What is the equation between the x and y coordinates of the projectile?

ehild

jamesblim168
what is the equation? what formula are you using to get the initial velocity?

Homework Helper
That you have to know. What equations are there for projectile motion?

ehild

jamesblim168
but i still have to get the time for me to calculate initial velocity right? then how can i get the time? why is this sooo confusing... sorry guys...

jamesblim168
is this the right formula for getting the initial velocity?
Vo = V - at
Vo - initial velocity
V - Velocity
a - acceleration
t - time

azizlwl
but i still have to get the time for me to calculate initial velocity right? then how can i get the time? why is this sooo confusing... sorry guys...

1. Given range(distance first and last wheel). From this you can calculate horizontal the velocity Vx.

2. From this velocity you find the maximum height the man goes above the middle wheel assuming equally spaced wheels.

3. Add this height to the height from top of the wheel to the gun.

4. You have total height to cover with 45degree projectile

voko
What we have been saying is that you cannot calculate anything now, because the problem requires that you make certain assumptions on the arrangement. All you know is how wide the three wheels (= W) to fly over, and how high (= H) they are. But you do not know how far from the wheels the launch pad and the target net are. These unknown distances and W and H will together result in certain restrictions on the equations of motion, from which you could deduce the minimum initial velocity.

jamesblim168
where are you masters?

jamesblim168
so your saying il make assumptions so there's no wrong answer here? outcome will depend on my assumptions?

jamesblim168
can anyone solve this?