a small block with a mass 0f 0.33 kg is attached to a cord passing through a hol
ID: 1780346 • Letter: A
Question
a small block with a mass 0f 0.33 kg is attached to a cord passing through a hole in a frictionless, horizontal surface. The block is originally revolving at a distance of 0.50 m from the hole with a speed of 0.70 m/s. The cord is then pulled from below, shortening the radius of the circle in which the block revolves to 0.10 m. At this new distance, the speed of the block is observed to be 2.80 m/s.
a) What is the tension in the cord in the original situation when the block has speed v = 0.70 m/s?
b) What is the tension in the cord in the final situation when the block has speed v = 2.80 m/s?
c) How much work did the person who pulled the cord do? Compare this to the work performed when you lift a quarter-pounder hamburger to take a bite. (Remember that the 14-lb refers to the weight of the beef-patty, you must also include the rest of the burger in your comparison.)
Explanation / Answer
a) T = m v2 / r
= 0.33 * 0.702 / 0.50 = 0.323 N
b) T' = m v2 / r
= 0.33 * 2.802 / 0.10 = 25.87 N
c) From work energy relation, W = delta KE
= 1/2 m v2 -1/2 m u2
= 1/2 * 0.33 [2.82 - 0.702]
W = 1.21 J
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