a block is pushed up a slope by a force parallel to te slope. What is the kinetic coefficient between the block and the slope?

Question

Problem:



A 45.0 kg block is being pushed up a 14.0° slope by a force of 280.0 N which is parallel to the slope. What is the coefficient of kinetic friction between the block and the slope, if the block is moving up the slope at a constant velocity? 

Additional Question (not necessary, but appreciated)

1. How is the free body diagram made?
2. Which formulas should be used and in what order?
3. If you have any advice on solving problems like this or identifying what needs to be found, its welcome!

Physics 1

Answer 1

THe first step is to make a free-body diagram of the block. Draw it on the slope first, then replace the slope with the forces acting on the block, and remove the slope, leaving only the block and forces.

Second, use a convenient coordinate system... since the forces are acting parallel to, and perpendicular to the slope (at 14 deg.above horizontal) and that is the direction of the motion, make your x-axis parallel to that slope.

Principal one is that the block is not accelerating (a=0) so what is the sum of the forces in the x-direction? in the y direction?

Principal two is that the forces acting on the block by the slope itself can be referred to as the Normal force, perpendicular to the slope, and friction, parallel to the slope and acting against the direction of motion.

Principal three is that the force of friction is k * Fn... k is the coefficient of friction, and Fn is the Normal force acting on the block by the slope.

Principal four is that since the block is not moving at all (therefore not accelerating) in the y-direction, therefore the sum of the forces in the Y-direction = ??

Principal five is that the logical result of principal four is that the component of the weight of the block acting perpendicular to the slope must be equal and opposite to the Fn Normal force. Use vector diagrams to break up the Weight of the block into the component perpendicular to the slope and the component parallel to the slope (resisting the force pushing the block)

Best Wishes!

Michael Wiseman-Floyd

Wyzant Pro Tutor