A 10 lb block was resting on a horizontal table. The coefficient of static frict

Question

A 10 lb block was resting on a horizontal table. The coefficient of static friction between the block and the table is 0.8 and the coefficient of dynamic friction is 0.7. A force barely sufficient to overcome the static friction is applied to the block.

If the force is not changed how fast is the block moving 5 seconds later?

1) What is the block's mass in SI units?

2) What is the block's weight in SI units?

3) What is the total force acting on the block in the verticle direction?

4) What is the normal force acting on the block?

5) What is the maximum sttic friction between the block and the table?

6) What force needs to be applied to barley overcoe the maximum static friction?

7) What is the magnitude of the dynamic friction between the moving block and the table?

8) If the force determined in part 6 is applied and not changed, what is the magnitude of the total force acting on the moving block in the horizontal direction?

9) What is the accelleration of the block?

10) What is the initial speed of the block?

11) What is the final speed of the block?

Explanation / Answer

1)1 lb = 0.454 kg

10 lb = 4.54 kg

Hence, m = 4.54 kg

2)W = mg

W = 4.54 x 9.8 = 44.49 N

Hence, W = 44.49 N

3)The net force in vertical direction would be zero, because the gravuty has got a normal reaction.

4)N = mg

N = 44.49 N

5)Fs = us N

Fs = 0.8 x 44.49 = 35.59 N

Hence, Fs = 35.59 N

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