anybody good at physics?

[Hulud]

oh shit really? Dude thanks man! All that in one step, you are a genius!

i try i try

[ProjectWidow]

shit I still have like 5 more problems left, anyone?

[ironchef]

Shoot again, but see if theres formulas, i cant remember them for shit lol.

[ProjectWidow]

Shoot again, but see if theres formulas, i cant remember them for shit lol.

A 2.3 kg rock initially at rest loses 403 J of potential energy while falling to the ground. Assume that air resistance is negligible.
(a) Calculate the kinetic energy that the rock gains while falling.
___J
(b) What is the rock's speed just before it strikes the ground?
___m/s

The main formula is PE(before) + KE (before) = PE (after) + KE (after)
where PE = mgh
and KE = 1/2mv^2



and another one that should be easy
A cannonball is fired at 50 m/s at an angle of 30 degrees. How high does it go? (Hint: determine the vertical velocity, and use conservation principles.)
___m
I just cant seem to figure it out. I tried doing trig functions but it doesnt work out

[D16Civic]

i dont remember exactly, but doesnt Potential energy just turn into kinetic energy once it starts moving, therefore a. would be 403 J. Its been a little while, so thats probably wrong, but who knows.

[ProjectWidow]

i dont remember exactly, but doesnt Potential energy just turn into kinetic energy once it starts moving, therefore a. would be 403 J. Its been a little while, so thats probably wrong, but who knows.

oh shit!! It was so easy, it was hard. Thanks bro

I would give you rep points but it says I have to spread some love first

[D16Civic]

is b. 18.72 m/s
PE=KE=403=.5(2.3kg)v^2

[ProjectWidow]

figured out how high the cannon goes. was using cosine function instead of sine

[ironchef]

figured out how high the cannon goes. was using cosine function instead of sine

Was it 127?

[ProjectWidow]

is b. 18.72 m/s
PE=KE=403=.5(2.3kg)v^2

you would think, right? But I just checked and thats wrong

[ProjectWidow]

Was it 127?

no, it went 31.887
since you find the sine function which is 50sin30
then you use 1/2w^2=gh (KE=PE)

[ProjectWidow]

is b. 18.72 m/s
PE=KE=403=.5(2.3kg)v^2

woops, you are right man! My bad. i put in 18.27 instead of 18.72.

Thanks guys!!

[ironchef]

Wow my physics skills have gone to crap, and to think i have to take physics sometimes in the next 3 semesters .

[ProjectWidow]

Wow my physics skills have gone to crap, and to think i have to take physics sometimes in the next 3 semesters .

hey its alright. Look at me! Im in physics and cant seem to get a few easy problems done. It just sucks not being able to pay attention at the end of the day

[ironchef]

hey its alright. Look at me! Im in physics and cant seem to get a few easy problems done. It just sucks not being able to pay attention at the end of the day

Yea I hear ya, I was barely keeping my head up in history today, its not even that its so boring, but its just towards the end of the day and im just like let me leave haha.

[ProjectWidow]

Yea I hear ya, I was barely keeping my head up in history today, its not even that its so boring, but its just towards the end of the day and im just like let me leave haha.

exactly the way I am, lol

alright last one for the night
Justin throws a 12.0 g ball straight down from a height of 2.0 m. The ball strikes the floor at a speed of 7.5 m/s. What was the initial speed of the ball? Assume that air resistance is negligible.
____m/s

[ironchef]

exactly the way I am, lol

alright last one for the night
Justin throws a 12.0 g ball straight down from a height of 2.0 m. The ball strikes the floor at a speed of 7.5 m/s. What was the initial speed of the ball? Assume that air resistance is negligible.
____m/s

Im going to go with either 9.76 or 0 being that it might be a trick question

[D16Civic]

im saying its 4.12 m/s

[ProjectWidow]

im saying its 4.12 m/s

you are the fuckin man!! Whenever I can give you more rep points, you got em!


thanks guys, you both were a big help!!

[D16Civic]

no problem, glad i could help

[ironchef]

How did you solve that one?

[D16Civic]

i just used the formula v(final)^2=v(initial)^2 + 2*a*distance where you are trying to find v(initial). The mass isnt needed since objects will fall at the same rate no matter what their mass is. So then its just plugging in the numbers.
Square root of [(7.5)^2 - 2(9.81)(2)]

[ironchef]

Whoopsie i think i added the 2*9.8*2 instead of subtracting ,