Problem 1

A block is released from rest on a plane inclined at

\theta=30^\circ

. The kinetic-friction coefficient is

\mu_k=0.20

and

g=9.8\,\mathrm{m/s^2}

. Contact is maintained and friction opposes sliding; take the positive axis down the plane. (a) Find the first requested quantity. (b) Find the second quantity. (c) Determine the final result and check its units. (a) Find the normal reaction. (b) Find the kinetic-friction force. (c) Find the acceleration and determine its direction.

problems.proof.stepOf

problems.proof.prevStep problems.proof.nextStep

f_k=\mu_kN=\mu_kmg\cos\theta

problems.proof.analysis

This equation expresses the physical law governing the system. It incorporates the stated constraint rather than treating the relevant quantities as independent.

problems.proof.pitfall. Check the sign convention and physical case carefully; do not use a formula for a different motion or geometry.