A frictionless30degrees incline should provide an acceleration of 4.90m/s2 down the incline. A student with a stopwatch finds that an object, starting from rest, slides down a 15m very smooth incline in exactly 3s. Is the incline frictionless?
a = 2d/t^2 = 2*15/(3*3) = 3.333 m/s2
g sin30 = 9.8 * 0.5 = 4.9
3.33 < 4.9
====> therefore the incline is not frictionless.