What is wrong with my math here? [Kinematics]

Kuzon · Mar 25, 2016

Homework Statement

Textbook problem diagram: a skateboarder moving right at 6.50 m/s on a track slanted upward at angle θ = 55.0°, leaving the end and following a projectile arc. Height labeled 0.660 m from the ground to the track end, and maximum height labeled H above it.

Open image in new tab to enlarge please :)

Homework Equations

I was trying to compare the initial KE/PE with the final KE/PE in order to find out how far the skateboarder rose but the solution was wrong for some reason?

Keep in mind the skateboarder is traveling along the HORIZONTAL portion of the ramp at 6.5m/s so when he gets to the top of the ramp he will only be traveling at 5.77m/s by my calculations.

The Attempt at a Solution

Handwritten physics working on lined paper: energy conservation setup with 1/2 m(5.5)^2 and 1/2 m(6.8)^2 + mgh terms, leading to v = 5.77096, then v^2 - v_i^2 over 2g giving -4.7272/(2(9.8)) = 1.14 m.

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SteamKing · Mar 25, 2016

Somehow, the skateboarder's initial horizontal velocity morphed from 6.5 m/s to 6.8 m/s in your calculations of KE/PE. Bad handwriting, perhaps?

Kuzon · Mar 25, 2016

SteamKing said:

Somehow, the skateboarder's initial horizontal velocity morphed from 6.5 m/s to 6.8 m/s in your calculations of KE/PE. Bad handwriting, perhaps?

WOW, thanks so much. I was killing myself over this question and probably spent ~3 hours trying to rack my brain around it even though it's basic physics.

What is wrong with my math here? [Kinematics]

Homework Statement

Homework Equations

The Attempt at a Solution

Discussion

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