Block sliding down an inclined plane and gravity

AI Thread Summary
A 5.0 kg block is sliding down a 12-degree inclined plane, and the coefficient of kinetic friction is 0.310. The calculated frictional force exceeds the gravitational component acting down the slope, indicating that the block is decelerating despite moving downward. This situation suggests that net work done by friction and gravity is negative, as friction opposes the motion. The discussion highlights the need to consider initial forces that may have imparted velocity to the block. Understanding these dynamics is crucial for accurately calculating the work done by both friction and gravity.
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Homework Statement


There is a 5.0kg block sliding 1.5m down an inclined plane 12 degrees from the horizontal. the coefficient of kinetic friction is 0.310. Whats is the work done on the block by friction and gravity?


Homework Equations


F=ma, W=fd, fk=uk*N


The Attempt at a Solution


So, i calculated the frictional force to be mgcos(12)\mu_{k}, but when i found the component force of gravity in the opposite direction (mgsin(12)), i found that the force of friction was bigger than it. I think I am just overlooking something major, but i can't see what i did wrong.
 
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You didn't do anything wrong. You're right... the friction is greater than the component of gravity... this means the acceleration is up the plane...

So it is sliding downwards, but slowing down. net work done by friction and gravity will be negative.

Go ahead and calculate the work by friction and gravity.
 
DOH! of course. I feel really dumb now. Thanks for your help.
 
If I have understood the above correctly, some initial force must have been provided before it moved. That would have imparted the velocity, and the unbalanced force will decelerate it.
 

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