A 5.0 kg block starts at rest and slides down a frictionless track except for a

Question

A 5.0 kg block starts at rest and slides down a frictionless track except for a small rough area on a horizontal section of the track. It leaves the track horizontally, flies through the air, and subsequently strikes the ground at a distance of L=1.8m from the base of the track. A) what is the velocity of the block as it leaves the track? B) how much work is done by the force of friction as the block moves through the rough area? C) At what height h above the ground is the block released? D) How much work is done by the gravity force through the entire process? http://i49.tinypic.com/2letf.jpg

Explanation / Answer

To get to the beginning of this, you have to start at the end. The block flies 1.3 meters forward while falling 2.1 meters. You can calculate the time to fall 2.1 meters from a standing start (t=?2gd), and knowing the time and 1.8 meters travelled you get the speed from v = d/t. From the speed at the dropoff, you calculate the kinetic energy per mass. Before the dropoff the block travels 1.3 meters over the stretch of ?=0.3. The deceleration will thus be ?g; you can calculate from this the energy lost per mass (e/m = a

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