# I think my physics teacher doesnt have a clue

## Homework Statement

we did a experiment in class shooting marbles and taking measurements. The size of the Marble is .0019 meters and with a photo gate timed it at .0037 secs. Giving me a initial speed of .5135 m/s2. I am now trying to find time. with the angle being 70 degrees

## Homework Equations

She gave us this equation to find time T= Velocity*Sin(angle)/Gravity.

## The Attempt at a Solution

I have tried several times looking at the units. We did the experiment and the distance it traveld was roughly 1.62 meters. KNowing this i figured the time to be roughly 3.15s. But using the formula she gave me i cant come up with the same answer what am i doing wrong?

## Answers and Replies

Filip Larsen
Gold Member
Welcome to PF!

The equation you mention gives the time the marble takes to travel from the photo gate to the top of its trajectory (ignoring air resistance). If you want the time for the "whole" trip (assuming it lands at the same height as the photo gate), you should use twice this value.

But I think you must have made a measurement error somewhere, because a particle with initial speed of around 0.5 m/s will only take around 0.1 s to fall and it will only reach a maximum height around 0.01 m. To get a trip time of around 3.15 s the initial speed should have been around 16.5 m/s which gives a maximum height around 12.2 m.