8/8/2019 IJSO answer ( 28-10-10)

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IJSO QUESTION WITHANSWER (28-10-10)

1. Which one of the following when simplified isnot equal to one ?(A) tan18 tan 36 tan 54 tan 72(B) sin219 + sin271

(C) 28cos

62sin2

48eccos

42sec

(D*) none of these

Sol. (A) tan18 36 tan54 tan72= tan18 tan72 tan36 tan54= tan18 cot18 tan36 cot36= 1(B) sin219 + sin2 71= sin219 + cos219= 1

(C)28cos

62sin2

48eccos

42sec

62sin

62sin2

42sec

42sec

2 1 = 1so all (A), (B), (C) are equal to 1 so (D) noneof these is the correct option

2. A ball rolls off the top of a staircase with ahorizontal velocity u m s1 . If the steps are hmetres high and w metres wide the ball with hitthe edge of the nth step if :

(A) n = 2

2

hu2gw (B*) n = 2

2

gwhu2

(C) n =hgw

u22

2

(D) n =g

uhw2 22

Sol. The horizontal and vertical distances moved bythe ball while just hitting the edge of n th stepare clearly nw and nh respectively. Let the timetaken by the ball for these horizontal andvertical displacements b t . Then

nw = ut ; nh = 0 +2

1gt2

Eliminating t between these equations, weget

nh =2

1g

2

u

nw

or n = 2

2

gw

hu2

3. A hydrocarbon with molecular formula C8H18gives only one monochloro derivative. The hy-

drocarbon is

(A) n-octane.

(B) 2-methylheptane.

(C) 2,2,4-trimethylpentane.

(D*) 2,2,3,3-tetramethylbutane.

Sol. Since the hydrocarbon C8H

18gives only one

monochloro derivative, it means all 18 hydro-

gen atoms are equivalent, which is possible only

in case of 2,2,3,3-tetramethylbutane

4. The sensation of sight in human brain is

perceived by.

(A) Optic lobes

(B*) Occipital lobes

(C) Association area of frontal lobes

(D) Somaesthetic area of parietal lobes