# Projectile Motion - object that is shot at an angle of 55 degrees

## Homework Statement

Projectile motion
I have an an object that is shot at an angle of 55 degree's. (the velocity listed next to it was 35 m/s, which was not listed as Vo but I think I have to assume it is?) It is launched from the ground. it is meant to land to hit a button that is elevated by 32 feet. we have to find the distance away from the button to launch the object in order to hit the button.

## Homework Equations

Delta x= Vo * t
delta y = 1/2gt^2 + Vo * t

## The Attempt at a Solution

I tried a bunch of things that did not help me come to any sort of conclusion about the distance (x)

Last edited:

gneill
Mentor
Please show us what you've tried.

Homework Helper
Gold Member
For the ## x=v_x t ##, you need to have ## v_x=v_o \cos(55^{\circ}) ##. Do you see why? ## \\ ## For the y equation, you need ## y=-\frac{gt^2}{2}+v_{yi} t ## where ## v_{yi}=v_o \sin(55^{\circ}) ##. The acceleration due to gravity is downward=thereby the minus sign. ## \\ ## Meanwhile, an important part you are missing is to separate the initial velocity ## v_o ## at an angle of ## 55^{\circ} ## into horizontal and vertical components. I have shown you this result in the equations above. ## \\ ## Now that I got you started, can you figure out what to do to answer the question they are asking? Here's a hint: Can you solve for ## y ## as a function of ## x ##? ## \\ ## Presently, the equations you have go through the point ## x=0,y=0 ## at ## t=0 ##. What is ## x ## when ## y=32 ## ? You need to determine the equation that gives you ## y ## as a function of ## x ##, and then you can answer that question.

Last edited:
Yellowkies_3275
Please show us what you've tried.
sorry i didn't fill it out properly. i think i have a solution to the question now though, so i was wondeering if this thread could be deleted

gneill
Mentor
sorry i didn't fill it out properly. i think i have a solution to the question now though, so i was wondeering if this thread could be deleted
After a thread has received replies, particularly where contributors have put in significant effort, our policy is to not remove the thread so that other members can benefit from the information.

Ray Vickson
Homework Helper
Dearly Missed

## Homework Statement

Projectile motion
I have an an object that is shot at an angle of 55 degree's. (the velocity listed next to it was 35 m/s, which was not listed as Vo but I think I have to assume it is?) It is launched from the ground. it is meant to land to hit a button that is elevated by 32 feet. we have to find the distance away from the button to launch the object in order to hit the button.

## Homework Equations

Delta x= Vo * t
delta y = 1/2gt^2 + Vo * t

## The Attempt at a Solution

I tried a bunch of things that did not help me come to any sort of conclusion about the distance (x)

Be very careful. If ##y## measures height above the ground, your formula ##\Delta y = v_0 t + \frac{1}{2} g t^2## will have the object accelerating rapidly upward, until it goes into outer space (because, conventionally, ##g## is a positive constant).

Be very careful. If ##y## measures height above the ground, your formula ##\Delta y = v_0 t + \frac{1}{2} g t^2## will have the object accelerating rapidly upward, until it goes into outer space (because, conventionally, ##g## is a positive constant).
How do I change the equation to keep it from accelerating into outer space?

Homework Helper
Gold Member
How do I change the equation to keep it from accelerating into outer space?
You put a minus sign in front of the ## \frac{g \, t^2}{2} ## term. ## g=+9.8 ## m/sec^2, but ## a=-9.8 ## m/sec^2. ## \\ ## Otherwise, your equation for ## y ## has the form ## y=At^2+Bt ## with ## A>0 ## , so that ## y ## will get increasingly larger with time ## t ##.

Yellowkies_3275
You put a minus sign in front of the ## \frac{g \, t^2}{2} ## term. ## g=+9.8 ## m/sec^2, but ## a=-9.8 ## m/sec^2. ## \\ ## Otherwise, your equation for ## y ## has the form ## y=At^2+Bt ## with ## A>0 ## , so that ## y ## will get increasingly larger with time ## t ##.
You are a life, saver thank you very much for your explanations