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A plank with a box on it at one end is g...

A plank with a box on it at one end is gradually raised about the other end. As the angle of invlination with the horizontal reaches `30^@` , the box starts to slip and slides 4.0 m down the plank in 4.0s.The coefficients of static and kinetic friction between the box and the plank will be, respectively:
.

A

0.4 and 0.3

B

0.6 and 0.6

C

0.6 and 0.5

D

0.5 and 0.6

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