Quiz #7 - Energy Analysis in Physics 2050, Fall 2011 - Prof. Max Wyman, Quizzes of Physics

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PHYS 2050

Fall 2011 Quiz #7 - Energy Analysis Instructions: answer all problems and show all relevant work needed to find solution. Circle your final answer. Some (possibly) useful equations and constants Σ F = m a! Ff = μkN# Ff = μsN ac = v^2 /r W = ΔK K = ½mv^2 W = F·d W = ∫ F· d r v^2 = v·v ΔEsystem = ΔK + ΔU + ΔEint ΔEint = Fkd Wconservative = -ΔU P = dE/dt Ug = mgh Us = ½kx^2 Problems:

1. (10 pts ) A sled of mass m is given a kick on a frozen pond. The kick imparts to the sled an initial speed of v. The coefficient of kinetic friction between sled and ice is μk. (A) Using energy considerations find the distance the sled moves before it stops in terms of m , v , g , and μk. (B) In terms of the m and v , what is the change in internal energy of the sled/pond system during the slowing process?
2. (10 pts) A light rigid rod of length of 60.0 cm is pivoted at it’s top end by a frictionless horizontal axle. A ball of mass 4.0 kg is attached to the other end. You strike the ball imparting a horizontal velocity to it so that it moves in a complete circle. What is the minimum speed you would need to impart to the ball at the bottom of the circle to get it to swing in a full circle?