Physics Help Forum Work on an inclined Plane- Check if right please?

 Oct 11th 2008, 02:11 PM #1 Junior Member   Join Date: Oct 2008 Posts: 16 Work on an inclined Plane- Check if right please? A 5.00 kg package slides 1.50 m down a long ramp that is inclined at 12 degrees below the horizontal . The coefficient of kinetic friction between ramp and package is 0.310.* c) What is the net work done on the package? Will it just be -22.3 J since the normal force and the weight is perpendicular to the x direction.* d) If the package started sliding with a speed of 2.20 m/s, find it's final speed. net work = change in KE net work = 1/2 m (vf^2-vi^2) = 1/2(5 kg) (vf^2 - 2.20^2) Vf = 1.39 m/s (Right?)
 Oct 11th 2008, 03:27 PM #2 Member   Join Date: Aug 2008 Location: Norway Posts: 43 If I've understood your question correctly, the force of gravity isn't perpendicular to direction the package is moving. Therefore it's also doing work. $\displaystyle W_{net}=W_R+W_G=- \mu mgcos(12) \cdot s+mgsin(12) \cdot s$ The normalforce is perpendicular to the direction it's moving. Last edited by Aslak; Oct 11th 2008 at 04:05 PM.
Oct 12th 2008, 09:35 AM   #3
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Join Date: Oct 2008
Posts: 16

 Originally Posted by Aslak If I've understood your question correctly, the force of gravity isn't perpendicular to direction the package is moving. Therefore it's also doing work. $\displaystyle W_{net}=W_R+W_G=- \mu mgcos(12) \cdot s+mgsin(12) \cdot s$ The normalforce is perpendicular to the direction it's moving.
Could you say work done by weight:

Ww = W x X cos theta
Ww = mg x X cos theta
Ww = (5 kg) (9.80 m/s^2) (1.50 m) cos 12

 Oct 13th 2008, 11:16 AM #4 Member   Join Date: Aug 2008 Location: Norway Posts: 43 Wcos12 is the component of the weight perpendicular to displacement. Wsin12 is the component of the weight in the direction it's moving. Making a sketch often helps. $\displaystyle W_w=mgsin(12) \cdot s=5,0 \cdot 9,8 \cdot sin(12) \cdot 1,5 \approx 15,3 \ J$

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