Physic Labs

Problem 1

A small block of mass m=2.0 kgm=2.0\,\mathrm{kg} is released from rest at the top of a straight, smooth plane inclined at α=30∘\alpha=30^\circ to the horizontal. It travels a distance s=10.0 ms=10.0\,\mathrm{m} measured along the plane. Take g=9.80 m s−2g=9.80\,\mathrm{m\,s^{-2}}, neglect air resistance, and choose downhill as positive. (a) Find the block’s acceleration and the normal force exerted by the plane. (b) Find the travel time and its speed at the bottom. (c) Find the work done by gravity and its average power during the descent.
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mgsin⁡α=mamg\sin\alpha=ma
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Down the plane, gravity contributes mgsin⁡αmg\sin\alpha; the normal force has no component along this axis. Newton’s second law therefore gives the displayed equation.

problems.proof.pitfall. Do not project gravity onto the wrong axis: the normal force has no component along the slope and does no work during the motion.