# Re Trainee teacher project

Discussion in 'Mathematics' started by ELLIS1980, Dec 31, 2011.

1. ### ELLIS1980

Hello, I am a trainee teacher currently doing an SKE via Brighton Uni. I have a project involving a hand held catapult. Am i correct in thinking i cannot calculate the range a projectile can be fired without having either time or initial velocity? I have Mass, acceleration and force already and have found a similar project involving a spud gun from which i can get muzzle velocity but not initial? Any help would be much appreciated.

Kind Regards ELLIS1980

2. ### DMNew commenter

I answered your last question on this topic. Can I suggest you borrow an M1 or M2 textbook (depending on the specification) and read up on projectiles? You will soon see that the quantities you claim to have measured are of little use here as, ignoring air resistance, the acceleration of a falling object is independent of its mass and is fixed at 9.81 metres per second squared downwards.

3. ### bcooper87

Hey,

What are you trying to find out and how does the catapult work? Could you not treat the end of the muzzle as zero? The muzzle velocity would then become the "initial velocity" and you could work out how far the object would travel from the end of the muzzle then add on the length of the barrell?

4. ### bcooper87

"You will soon see that the quantities you claim to have measured are of little use here "

If I stretch an elastic band across my finger and thumb and try to a projectile flying I will send a cannon ball the same distance as a scrunched up peice of paper? Ok the falling will be more or less the same but you need to take into account getting them going in the first place, so i reckon mass and force are important.

6. ### ELLIS1980

Hi,
i bought the catapult, so yes it works, Ive measured force in pounds by measuring the stretched elastic and converted to newtons, then ive got 5 different objects golf ball, ball bearing etc. from which ive calculated weight mass etc.
From this ive calculated acceleration and then hashed a formula for a gun to get muzzle velocity. Using this ive got some predictions for range but know that whilst my ball bearing and tennis ball have the same mass there not going to fire the same distance 150m?
Im thinking i will run experiment so will then have range and work it back? to check my velocity and force and then may try and see if i can take into account air resistance etc to justify the actual findings?
but if know anymore formulas or methology it would be much appreciated.

Happy new year!

7. ### ELLIS1980

Hi DM, thank-you for your help, ive found an M2 reference in which its got some really clear formulas.
Im thinking i will have to try how far i can fire the object so that i have range then work back to get velocity and time?
Not the way i thought project was going to go but hey ho its all a learning curve?
Cheers Dan and have a good new year.

8. ### DMNew commenter

Happy New Year Dan. I'm still not entirely sure what you are trying to do but you seem to be enjoying yourself anyway!