Question

7. Aplank balances horizontally on a log of wood, which acts as a pivot.
A girl sits on one end of the plank, and her brother pushes down on the other end to make the plank
bulance horizontally. Fig. 7.1 shows the arrangement.
pivot
1.2 m=distance form the pivot to the girl
1.6 m=distance form the pivot to the boy
weight of girl= 404N
Fig 7.1
(a)
Calculate the moment of the girl's weight about the pivot

Answer 1

Answer:

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Answer 2

Given:

Aplank balances horizontally on a log of wood, which acts as a pivot. A girl sits on one end of the plank, and her brother pushes down on the other end to make the plank.

To find:

Calculate the moment of the girl's weight about the pivot.

Explanation:

Static coefficient of friction is $tan 30^{0}$$=0.577$≈$0.6$

For kinetic friction, $ma=mg sin30-f=mg sin 30-mg cos 30$

$a=g sin 30-cos30--------(1)$

and also using $S=ut+1/2at^{2}$

$1.2=0+(1/2)a(1.2)^{2}$

$a=0.5 m/s^{2}$

Now from (1)we get $,0.5=10(1/2)-10(\frac{\sqrt{3} }{2}$

$\frac{4.5}{5\sqrt{3} }=0.5$

Answer:

Therefore, the girl's weight about the pivot is 0.5