Physic Labs

Problem 1

A block of mass m=4.0 kgm=4.0\,\mathrm{kg} starts from rest and slides s=6.0 ms=6.0\,\mathrm m down a 30∘30^\circ incline. The kinetic-friction coefficient is μ=0.10\mu=0.10; take g=10 m s−2g=10\,\mathrm{m\,s^{-2}}. The plane is fixed and the block remains in contact with it throughout the slide. The coefficient μ\mu is constant along the path, and kinetic friction opposes the motion. The block moves in a straight line down the plane with constant acceleration from its starting point to the stated endpoint. (a) Find the normal force and the acceleration along the plane. (b) Determine the speed at the end of the descent. (c) Calculate the time for the slide, assuming constant acceleration.
problems.proof.stepOf
problems.proof.prevStepproblems.proof.nextStep
a=4.13 m s−2a=4.13\,\mathrm{m\,s^{-2}}
problems.proof.analysis

Substituting the angle and friction coefficient gives a positive acceleration, confirming that the block speeds up downhill. The mass cancels because both driving and friction forces are proportional to it.