Change in Potential Energy: What am I doing wrong?

AI Thread Summary
The discussion focuses on calculating the change in potential energy for a block moving up an inclined plane. The user correctly calculates the change in kinetic energy as -124.5 J but struggles with the potential energy calculation. They initially use the sine of 30 degrees incorrectly, resulting in an incorrect potential energy value of 56.1 J. The key issue identified is that the calculator was set to the wrong mode, affecting the sine calculation. Ensuring the calculator is in degree mode is essential for accurate results.
Fittleroni
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Homework Statement


A 4.20 kg block is set into motion up an inclined plane with an initial speed of v0 = 7.70 m/s (Fig. P7.25). The block comes to rest after traveling 3.00 m along the plane, which is inclined at an angle of 30.0° to the horizontal.

1. For this motion, determine the change in the block's kinetic energy.
DeltaK = 1/2m(vf^2-vi^2)^2=-1/2mvi^2= -124.5J

This next question is the portion I am having problems with:

2. For this motion, determine the change in potential energy of the block-Earth system.

Homework Equations



DeltaU = mg(3.00)sin30.0

The Attempt at a Solution



=(4.20)(9.8)(3.00)(0.454)
=56.1

So what is wrong with my answer??
 
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What's the sine of 30 degrees?
 
Fittleroni said:

Homework Equations



DeltaU = mg(3.00)sin30.0

The Attempt at a Solution



=(4.20)(9.8)(3.00)(0.454)
=56.1

So what is wrong with my answer??

Before you begin calculations involving trig functions, always check the mode your calculator has been left in. The sine of 30 grads is 0.454; you need to reset the input mode to degrees...
 

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