A spring of unstretched length L 0 = 0.20 m and spring constant k = 80 N/m is co
ID: 1488921 • Letter: A
Question
A spring of unstretched length L0 = 0.20 m and spring constant k = 80 N/m is connected to a block with M = 12 kg, which is supported by a horizontal floor. Initially, the spring is stretched to a distance L1 = 0.50 m and released from rest. The coefficient of static friction between the floor and the block is 0.45. The block is observed to come to rest at a distance L2 = 0.26 m.
1.What is the initial potential energy U1 stored in the spring?
2.What is the magnitude of the frictional force Ff on the block in its final position?
3. Refer to the situation in Question 27. How much work Ws is done by the spring in moving the block from L1 to L2?
M= 12 kg 2 lnitial Position Final PositionExplanation / Answer
1) U1 = 0.5*k*x1^2 (here x1 is initial extension)
= 0.5*80*(L1 - LO)^2
= 40*(0.5 - 0.2)^2
= 3.6 J
2) here, friction = force exrted by the spring
Ff = k*x2 (here x2 is final extension)
= k*(L2 - Lo)
= 80*(0.26 - 0.2)
= 4.8 J
3) Workdone by the spring = 0.5*k*(x2^2 - x1^2)
= 0.5*80*(0.08^2 - 0.3^2)
= -3.334 J
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