Saturday
December 20, 2014

Homework Help: Physics

Posted by Brandon on Tuesday, March 26, 2013 at 7:38pm.

Your artist friend's new work is a simple, high-impact kinetic sculpture called 'Destruction.' A 200-kg steel block is hung from the ceiling by an 8-foot-long rope. A second rope is attached to the side of the block. The other end of this second rope is attached to a motor which is cleverly mounted so that the rope always pulls the block horizontally with a constant force. The block starts from rest, hanging straight down, and is pulled slowly by the motor until it is hanging at an angle of 30 from the vertical. The horizontal rope is then released and the block swings and crashes into a wall. Your friend knows you have taken physics and asks you the minimum energy that the motor must supply. You perform a test and determine that the block is in equilibrium when it has been pulled so that it hangs at 30 degrees from the vertical.

(a) What is the algebraic expression for the energy that must be supplied by the motor in terms of the length of the rope (L), the mass of the block (M), the angle of release (θ), and the gravitational field strength (g)? [Note: Don't enter an equation like "x=blah". Just enter the "blah" part. All letters are capital except for "g".]
(b) What is the numerical value of the energy that must be supplied by the motor (make sure to include units and put a space between the number and the units)?

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