# Trajectory Problem

#### Sciencerob

I just put in 500 and then 1000 as different variables and they yielded the same answer....

Checking the format the only thing that looks like it might be out of place is that I have it Sin(30)^2 rather than Sin^2(30). It wouldn't take it any other way. I did put gravity as a negative force though. Should it be positive in this case? I think it should be negative considering the trajectory is going upward.

#### kuruman

Science Advisor
Homework Helper
Gold Member
I just put in 500 and then 1000 as different variables and they yielded the same answer....

Checking the format the only thing that looks like it might be out of place is that I have it Sin(30)^2 rather than Sin^2(30). It wouldn't take it any other way. I did put gravity as a negative force though. Should it be positive in this case? I think it should be negative considering the trajectory is going upward.
The symbol "g" stands for "the magnitude of the acceleration of gravity" and is a positive number equal to 9.8 m/s2. As for your sine problems, I offered you a suggestion, use it or not as you see fit.

#### Sciencerob

I did use your sin*sin format and I removed the negatives from the gravity. Still getting the same results. I've doubled and triple checked, I did put in the right variables all the way through. I keep getting 6.88337

#### kuruman

Science Advisor
Homework Helper
Gold Member
I did use your sin*sin format and I removed the negatives from the gravity. Still getting the same results. I've doubled and triple checked, I did put in the right variables all the way through. I keep getting 6.88337
What are the "same results" that you are getting? Say you pick a muzzle speed of 300 m/s. What range do you get?

#### Sciencerob

When input 300 I get 6.86804. Anything above 70 starts to level off. I've done the following:

10 -> 3.332
20 -> 4.9
30 -> 5.71
40 ->6.12
70 ->6.599

#### kuruman

Science Advisor
Homework Helper
Gold Member
It looks like you are making a big mistake in your inputs, either the variables or the formula itself, probably the formula. I used Excel and here are a couple of benchmarks

v0 = 150 m/s, R = 2057 m
v0 = 300 m/s, R = 8023 m

I cannot help you any more. It is between you and your TI-89.

#### Sciencerob

Alright, I've moved to a computer with excel. If anyone would mind helping me out here (sorry for the trouble).

=(500*Sin(30)+Sqrt(500^2*Sin(30)*Sin(30)+2(44.1)(9.8)/9.8))*500cos(30)

is what I put in and it spits back out at me that I am doing something wrong..

#### kuruman

Science Advisor
Homework Helper
Gold Member
First off you need to put asterisks to denote multiplication. This 2(44.1)(9 .8) won't work.
Secondly, you need to put the angle in radians, not degrees.

#### Sciencerob

Almost there... I got it to work but when I put in 300 for Velocity I got a number around 40,000.

=(300*SIN(0.5236)+SQRT(300^2*SIN( 0.5236)*SIN(0.5236)+2*(44.1)*(9.8))/9.8)*300*COS( 0.5236)

That is my formula.

#### Sciencerob

Well, I do hope I can get a response quick before my school's library closes. If not Thanks for your help.

#### kuruman

Science Advisor
Homework Helper
Gold Member
Almost there... I got it to work but when I put in 300 for Velocity I got a number around 40,000.

=(300*SIN(0.5236)+SQRT(300^2*SIN( 0.5236)*SIN(0.5236)+2*(44.1)*(9.8))/9.8)*300*COS( 0.5236)

That is my formula.
You put this 9.8 in the wrong place. It should divide everything not just the radical.

### Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving