IIT JEE , AIEEE Forum - Physics , Mechanics

tarinbansal

A boat with scrap iron is floating in a lake. If the scrap iron is thrown in the lake, the water level will

A- Go up

B- Go Down

C- Remain unchanged

D- None of these

Please tell the ans alongwith explanation.

abhijeet_0201

shud be a

since when in boat the iron piece will add to weight of boat(vol of piece x density of iron xg)
when in water it will displace water equal to its volxdensity of water xg)
since density of iron is gr8er than water
so water will rise(i may be wrong0

tarinbansal

Yup dude,
U R wrong.
The ans is not A.

Its B but I think it shud be C.

shubham_sachdeva

qn.is not clear..wats iron scrap??

tarinbansal

pata nahi what do they mean by iron scrap.
Maine to ques as it is copy kar diya hai buk se.
Its up to U to think.

tarinbansal

The literal meaning of scrap is-

1. fragment: a small piece or remnant that has been detached or torn off from a larger piece
2. waste material: waste material, especially metal awaiting reprocessing
3. small piece: a very small piece of something

Maybe they want us to neglect the vol of iron scrap and if we neglect it, we will get the correct ans, that is, C.

abhijeet_0201

is the correct ans b or c

tarinbansal

The ans given is B.

shubham_sachdeva

oh...no i understand.....see

when dat scrap is in boat buoyant force was B(let it)..NOW WHEN dat scrap is thrown bouyant force will not change...thus if we put less weight then water level will be less...as compared to more weight in boat..B will be equal bcz scrap-less weight.only boat displaces water in both the cases. so B = const.

hope its clear now...

tarinbansal

Buddy,
I still think there is some prob.
See U cant neglect the mass of iron. When the iron was in the boat, the vol submerged will be more as compared to when iron is not in the boat.
SO in the first case, the buoyant force will be more than the second case.

shubham_sachdeva

arrey why ...small scrap=very less vol. as compared to the material of the boat...also, density factor plays role....well what i think i said ...wait for others to comment...

saketsahoo

fundas to apply here=

1.while an object is floating,it displaces liquid whose weight is equal to its own weight. hence if a denser object is sitting in a boat,it is displacing more volume of water than its own volume.

2.if a denser object is sitting sunk completely inside a liquid, it will displace liquid whose volume will be equal to its own volume.

hence the answer is b. hope it helped.

sid.shah.90

Ans (b)
Vol displaced by (boat+scrap) will b more than vol of water displ. by boat alone.....
And when submerged, scrap will naturally displ. vol = vol of scrap

Thus water level will go down

Pretty interesting..... what we intuitively think will happen is many a times wrong!!

anchitsaini

Well what I can think is this--

the boat with scrap iron would displace more water than boat alone+scrap alone. this is because boat + scrap iron would displace water equal to volume of boat submerged without stone(v1) +due to weight of stone(v2). however when scrap iron would be thrown. boat will displace water equal to v1 and scrap iron would sink hence it will displace v3=less water than what its weight would ie v3<v2, therefore v1+v2>v1+v3, thus the water level would fall.

Ask & Discuss Questions with Community & Experts