Question 227: Laws of Motion

Question

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

Accepted Answer

Coefficient of static friction,
$${\mu _s} = 	an 30^\circ  = {1 \over {\sqrt 3 }} = 0.577 \cong 0.6$$
$$S = ut + {1 \over 2}a{t^2}$$
$$4 = {1 \over 2}a{\left( 4 ight)^2} \Rightarrow a = {1 \over 2} = 0.5$$
[$$ \because $$ s = 4m and t = 4s given]
a = gsin$$	heta $$ Ã¢ÂÂ $${\mu _k}(g)\cos 	heta $$
$$ \Rightarrow {\mu _k} = {{0.9} \over {\sqrt 3 }} = 0.5$$

Answer

0.5 and 0.6

Answer

0.4 and 0.3

Answer

0.6 and 0.6

Answer

0.6 and 0.5

Laws of Motion

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