Homework Help: physics

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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