Posted by **Vishnu** on Wednesday, October 8, 2008 at 8:15pm.

A skier is gliding along at 1.13 m/s on horizontal, frictionless snow. He suddenly starts down a 13.1° incline. His speed at the bottom is 18.8 m/s. What is the length of the incline?

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Use his change in kinetic energy to get his loss of potential energy. The equation

g H = change in (V^2)/2

can be used to het the height change, H.

H and the slope angle can be used to get the length L of the incline.

H/L = sin 13.1

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My attempt:

H/L = sin 13.1

L = sin13.1 / H

= sin13.1 / 18.8 m/s

= 0.01 km = 10 m

Why is this answer incorrect?

Responses

physics - drwls, Wednesday, October 8, 2008 at 2:10am

Your equation L = sin13.1 / 18.8 m/s

is totally wrong. You cannot have a length on one side of an equation and 1/Velocity on the other side. It is not even dimensionally correct. You did not follow the method suggested. Where did the L = 0.01 km come from?

The change in V^2/2 is (18.8^2 - 1.13^2)/2 = 176.1 m^2/s^2

That equals the change in gH

The change in H is therefore

176.1 m^2/s^2 / 9.8 m/s^2 = 18.0 m

physics - Luckna, Wednesday, October 8, 2008 at 9:35am

This answer still shows up as incorrect

- physics -
**drwls**, Wednesday, October 8, 2008 at 8:23pm
I computed H for you. They asked for the length L of the incline. Did you do the final step to get L?

We usually don't do complete answers for students. We try to teach you the method to solve problems yourself.

- physics -
**bobpursley**, Wednesday, October 8, 2008 at 8:25pm
I agree with DrWLS.

- physics -
**Vishnu**, Wednesday, October 8, 2008 at 8:31pm
Can i have the formula for this step please?

- physics -
**bobpursley**, Wednesday, October 8, 2008 at 8:48pm
You know h is the height, you know the angle, and you are looking for the hypotenuse. Could the formula be the sine function?

- physics -
**Vishnu**, Wednesday, October 8, 2008 at 9:00pm
h =18.0 m

angle = 13.1°

hypotenuse = ?

Sine function formula is:

Opposite / hypotneuse

What is opposite?

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