3. A 5 lb block was resting on a horizontal table. The coefficient of static fri

Question

3. A 5 lb block was resting on a horizontal table. The coefficient of static friction between the block and the table mu is 0.8, and the coefficient of dynamic friction mu dynamic 0.7. A force barely sufficient to overcome the static friction is applied to the block. Full 30 points will be awarded, then partial credit will be awarded for the correct answer to the following question: i) What is the block?s mass in SI units? ii) What is the block?s weight in SI units? iii) What is the total force acting on the block in the vertical direction? iv) What Is the Normal force acting on the block? v) what is the maximum static friction between the block and the table? vi) what force needs to be applied to barely overcome the maximum static friction? vii) What is the magnitude of the dynamic friction between the moving block and the table? viii) If the force determined in part vi) is applied and not changed, what is the magnitude of the total force acting on the moving block in the horizontal direction? ix) What is the acceleration of the block?

Explanation / Answer

1) m= 2.27 kg

2) W = m*g = 22.25 N

3) Ftot = 0

4) N = m*g = 22.45 N

5) fs = us*N = 0.8*22.45 = 17.8 N

6) F = fs

7)fk = uk*N = 0.7*22.45 = 15.715 N

8) Fnet = fs - fk = 2.085 N

9) a = fnet/m = 0.918 m/s^2

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