IJSO answer ( 28-10-10)

IJSO QUESTION WITHANSWER (28-10-10) 1.

Which one of the following f ollowing when simplified is not equal to one ? (A) tan18º × tan 36º × tan 54º × tan 72º (B) sin219º + sin271º 2 sin 62º sec 42º  – cos 28 º cos ec 48 º (D*) none of these (A) tan18º 36º tan54 tan72 = tan18 tan72 tan36 tan54 = tan18 cot18 tan36 cot36 =1 (B) sin219 + sin2 71 = sin219 + cos219 =1

(C)

Sol.

(C)

nw = ut ; nh = 0 +

1 2 gt 2

Eliminating t between these equations, we get 2

2

2hu 1  nw    or n = nh = g  gw 2 2   u  

2 sin 62 sec 42  – cos 28 cos ec 48

3.

2 sin 62 sec 42  – sin 62 sec 42 2  – 1 = 1 so all (A), (B), (C) are equal to 1 so (D) none of these is the correct option

A hydrocarbon with molecular formula C8H18 gives only one monochloro derivative. The hydrocarbon is (A) n-octane. (B) 2-methylheptane. (C) 2,2,4-trimethylpentane.

2.

A ball rolls off the top of a staircase with a horizontal velocity u m s –1 . If the steps are h metres high and w metres metr es wide the ball with hit the edge of the nth step if : (A) n =

(C) n = Sol.

gw

2

2hu2

2u2 gw 2h

(B*) n =

2hu gw

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

Since the hydrocarbon C8H18 gives only one monochloro derivative, it means all 18 hydrohydrogen atoms are equivalent, which is possible only

2

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

2

2hw 2u2 (D) n = g

The horizontal and vertical distances moved by the ball while just hitting the edge of n th step are clearly nw and nh respectively. Let the time taken by the ball for these horizontal and vertical displacements b t . Then

4.

The sensation of sight in human brain is perceived by. by. (A) Optic lobes (B*) Occipital lobes (C) Association area of frontal lobes (D) Somaesthetic area of parietal lobes