A student throws a 1.00 kg ball upward into the air from an initial height of 0.

Question

A student throws a 1.00 kg ball upward into the air from an initial height of 0.00 meters. The ball reaches a maximum height of 3.00 meters, then falls back towards the ground. Assume the experiment takes place on the Earth's surface, with normal gravity. Assume that friction exerts a constant 2.00-newton force on the ball, and this force is always in the opposite direction to its motion.




Calculate the velocity of the ball when it is first thrown, and it's velocity as it returns to height=0 meters during its descent.

Calculate the kinetic energy of the ball when first thrown, and when it returns to height=0 meters

Calculate the work done by friction, and the work done by gravity during the flight of the ball.

Explanation / Answer

Given Mass of ball, m= 1.0 kg Height reached by the ball is , h = 3.0 m Frictional force , f = 2N By work energy theorem 1/2mvi^2 = mgh + fh 1/2mvi^2 = 1.0kg *9.8 m/s^2 *3.0m +2N *3.0m   ----1 vi = 8.41 m/s is the velocity of the ball when it is first thrown _______________________________________________ when the ball returns , by work energy theorem 1/2mv^2 = mgh - fh 1/2mv^2 = 23.4   --2 v = 6.84 m/s is velocity of the ball while returning _____________________________________________ KE is 1/2mvi^2 = 35.4 J from eq 1 KE while returning is , KE = 23.4 J   from eq 2 ______________________________________________ Work done by frictional force is w = f*s = 2N *3.0 m = 6 J Work done by gravity w = mgh = 1.0kg *9.8 m/s^2 *3.0m =29.4J

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