# Homework Help: Mechanical energy of a wooden block sliding down an incline.

1. Nov 18, 2013

### Kot

1. The problem statement, all variables and given/known data
A wooden block is on an incline with θ = 18.5 degrees. The angle was determined to be big enough that the wooden block would experience kinetic friction ( slides down the ramp). A photo-gate was used to measure the time it took for the block to move a certain distance. Five different trials are performed each time moving the block an increment of 10 centimeters away from the photo-gate. The distance of the block from the photo-gate are 0.2m, 0.3m, 0.4m, 0.5m, and 0.6m. The time it takes the block to pass the photo-gate is 0.31s, 0.31s, 0.313s, 0.36s, and 0.32s respectively. The velocities of each trial are about 0.18m/s for each trial. These values were calculated when I did my lab. I am supposed to calculate the kinetic energy, potential energy due to gravity, total change in mechanical energy and graph them in terms of the displacement.

2. Relevant equations
K=1/2mv2
U=mgh

3. The attempt at a solution
I was able to calculate the kinetic energy, potential energy and total change in mechanical energy of the wooden block. When I graphed displacement over change in total mechanical energy the graph was a line and had a negative slope. I assume that it is negative because the wooden block is losing energy due to friction while it travels down the incline so this results in a graph with a negative slope, is this correct?

2. Nov 18, 2013

### haruspex

Yes, but I'm surprised you always saw much the same speed. In fact, it seems to get slower as the run-up increases. Why is one time to 3 places of decimals and the others only to 2?
Seems to me your timings aren't precise enough to conclude much.

3. Nov 18, 2013

### Kot

I rounded the times down and accidentally left that part in. Looking back on the graph I do find the velocities decreasing slowly. I think this was due to the equipment because on some trials we would get a significantly faster velocity than the previous trials at the same distance.

4. Nov 19, 2013

### haruspex

Something might have been changing... getting warmer, or damper etc. Maybe you should have repeated the set of distances a few times to see if there were any trend against passing time.

5. Nov 19, 2013

### Kot

I will keep that in mind next time. I am unable to perform this experiment again at this time. I guess I have to state the error in my lab report.