Multiple choice

A 20 Kg box is pulled with uniform speed across a horizontal floor by a force directed 30o above horizontal.The coefficient of friction is 0.25.What is the magnitude of the force?

  1. 49.45 Newton

  2. 40.44 Newton

  3. 48.06

  4. 61.04
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A Correct answer
Explanation

f = Fcos 30oR = mg - Fsin 30of = $\mu$RFcos 30o = $\mu$(mg - Fsin 30o)F = $\mu$ mg / cos 30 + $\mu$ sin 30= 0.25 * 20 *9.8 / 0..866+0.25 *0.5= 49.45 Newton

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