2. A spring of spring constant 220 N/m is sitting on a table. You pick it up and

Question

2. A spring of spring constant 220 N/m is sitting on a table. You pick it up and stretch it so that it is 8.0 cm longer than it was on the table top. How much work did it take you to stretch the spring? (Hint: This work is just negative the work done by the spring on you!)

4. A block of mass 5.0 kg sits on a rough horizontal surface of coefficient of friction 0.12. A force of magnitude F = 10.0 N pulls on the mass at an angle of 30? above the horizontal. The block is observed to move across the surface a distance of 2.3 m. (a) What is the work done by the force F? (b) What is the value of the apparent weight of the block? (c) What is the work done by the normal force? (d) What is the work done by friction? (e) What is the work done by the gravitational force acting on the block?

Explanation / Answer

W= 1/2 kx2= 1/2*220*(0.08)2

= 0.704 J

2. a. W= F cos30 * 2.3= 19.92 J

b. mg- 10 sin30= 50-10*0.5= 45 N

c. W= 0 as it acts perpendicular to the direction of motion

d. same as part A = 19.92J

e. 0 as it acts perpendicular to the direction of motion

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