Help with a difficult math problem

[brycelesly]

I have an object that weighs 2 kg and is it dropped from a height of 30m. After it drops for 2 seconds, I need to find the kinetic and potential energy. Kintetic energy is represented by:

KE=.5mv^2 ; m = mass and v = velocity

Potential Energy is represented by:

PE= mgh ; m = mass, g = gravity (9.8), h = height

 

[brycelesly]

Bump. Please help me out~

 

[pappus]

I have an object that weighs 2 kg and is it dropped from a height of 30m. After it drops for 2 seconds, I need to find the kinetic and potential energy. Kintetic energy is represented by:

KE=.5mv^2 ; m = mass and v = velocity

Potential Energy is represented by:

PE= mgh ; m = mass, g = gravity (9.8), h = height

1. You can calculate the pot. energy when the object is at a height of 30 m.

2. When the object falls down the pot. energy is transformed into kin. energy. You need to know the speed of the object.
With a "uniformly accelerated movement" (I don't know the appropriate expression in English so I translated literally the German expression) you get:

$\displaystyle v(t)=a \cdot t$ with $\displaystyle a = 9.81\ \tfrac m{s^2}$
and
$\displaystyle s(t) = \frac12 \cdot a \cdot t^2$ where s is the travelled distance at time t.

3. Use these additional formulas to determine the kin. energy.

 

[DrPhil]

I have an object that weighs 2 kg . . .

No, you have an object with mass = 2 kg. Mass is a property of matter, and weight is the force of gravity acting on a mass. This is an important distinction. In SI units, mass is given in kg and weight is m*g, measured in N. I strongly recommend writing units on every number in every step of a calculation, and testing that you get the proper units in the result.

Pappus:
"uniformly accelerated movement" is good in English, but I would probably just say "with constant acceleration."
[I would like to see the word "downward" associated with the acceleration vector, as a reminder that a vector has a direction.]

 

[pappus]

...

Pappus:
"uniformly accelerated movement" is good in English, but I would probably just say "with constant acceleration."
[I would like to see the word "downward" associated with the acceleration vector, as a reminder that a vector has a direction.]

@DrPhil: Thank you for the clarification!

 

[Scremin34Egl]

You need to find the velocity at the 2 second mark. Use the equation vf=vi+at. Vi would be zero(object was dropped), solve for vf and then substitute it into 1/2mv^2 to get the kinetic energy.