Question

A block of wood of length 40cm and area of cross section 15cm^2 floats in water with 3/8 of its length above water.What is the density of wood?
(Density of water=1g/cm^3)

a) 0.256g/cm^3

b)0.526g/cm^3

c)0.625g/cm^3

d)0.650g/cm^3

Answer 1

@UnkleRhaukus @sauravshakya @Coolsector @hartnn @.Sam. @bahrom7893

Answer 2

@estudier @aroub

Answer 3

@ganeshie8 @Yahoo!

Answer 4

buoyancy force will be 15 * (5 * 40 / 8) * 1 * 9.8

upwards ..
now we have gravitational force Mg we can change Mg into (densityWood) * (volumeWood) * 9.8

so Mg is (densityWood) * 40 * 15 * 9.8

now Mg and buoyancy are equal since the wood stands still :

densityWood * 40 * 15 * 9.8 = 15 * 25 * 9.8
densityWood = 0.625

Answer 5

sorry for all the corrections .

Answer 6

you should read it all over again since i corrected stuff at the first line as well

Answer 7

@Coolsector I guess buoyancy force will be 15 * (3 * 40 / 8) * 1 * 9.8
^ Check this

Answer 8

@sauravshakya with 3/8 of its length above water
ABOVE WATER

Answer 9

use formula
v1.d1.g= v2. d2.g

Answer 10

You do not need gravity to solve this problem.

If an object sinks: volume of object = volume of (displaced) water
If an object floats: mass of object = mass of (displaced) water

Answer 11

obviously..but this will help dude to get insight of full fromula

Answer 12

@hartnn @sauravshakya @Yahoo!

Answer 13

i don't understand

Answer 14

So, u didnt get what @coolsector did?

Answer 15

no

Answer 16

plz tell me

Answer 17

Upthrust = weight of displaced liquid

Answer 18

U know that?

Answer 19

yaa

Answer 20

And when a body floats the weight of the body is equal to the upthrust

Answer 21

right?

Answer 22

right

Answer 23

Thus,
weight of the object=weight of displaced liquid
Mass of the object=mass of displaced liquid
density*volume of object=density*volume of displaced liquid
density*40*15 = 1* 5/8 *40 *15

Answer 24

Now, simplify it.

Answer 25

375

Answer 26

it gets 375

Answer 27

Nope it is 5/8

Answer 28

howz

Answer 29

Are u serious??????? Just do simple algebra.

Answer 30

\[1\times \times \frac{5}{8}\times40\times15\]

Answer 31

I know u can do it.