Find Optimum Angle of Launch: Calculate Velocity of Ball from Catapult

[monkeyguy31]

Hello, i have to work out the velocity of a catapult which i had to do for my AS Quality of measurement coursework where I'm trying to find the optimum angle of launch.

Homework Statement

A ball is fired from a catapult 0.5m above the ground, the ball hits the ground 1.45m away, the angle of launch is 45°. Calculate the velocity of the ball.

Homework Equations

v^2= u^2 + 2as

The Attempt at a Solution

Attempted it by plugging numbers into that equation but comes up with 37.6 m/s, whilst watching the catapult fire it took a few seconds to land so it couldn't be that fast, although after using Time = Distance/Speed it appears to be 3.9s which could be right but I'm not sure. Am I using the wrong equation i need to compare this to other angles but not sure what equation to use with angles.

 

[The Liberator]

Sorry, are you trying to find out the optimum angle of launch? Because you stated an angle in section one, the known data.

 

[monkeyguy31]

I was using 45° as an example, whilst doing the experiment I measured the distance traveled for 11 angles at 5° intervals from 20° to 70°. As 45° is the optimum angle excluding air resistance I'm going to work that one out first and compare to other angles. Should of included more detail.

 

[The Liberator]

How did you get the to answer of 3.9 seconds and 37.6 ms-^{1? From what you have given me in section one (the known data) I can only find the horizontal distance and the launch angle, and I cannot understand how you find your given answer from that. Is there a missing piece of data that you might have forgotten?}

 

[monkeyguy31]

I worked it out for myself, noticed i was making a huge error by putting the displacement in cm instead of metres, silly me.