Physics, Chemistry, Mathematics Forums

A carrom board(4ft * 4ft square)has the queen at the centre.the queen hit by the striker moves to the front edge,rebounds and goes in the hole behind the striking line.find the magnitude of displacement of the queen(a)from the centre to the front edge(b)from the front edge to the hole and(c)from the centre to the hole.pls explain in detail.

In order to stop a car in shortest distance on a horizontal road ,one should :

(a) apply the brakes very hard so that the wheels stop rotating

(b) apply the brakes hard enough to just prevent slipping

(c) pump the brakes(press and release)

(d) shut the engine off and not apply brakes.

A box contains 6 red,4 white and 5 black balls.A person draws 4 balls at random.Find the probability that among the 4 balls drawn there is atleast 1 ball of each color.


Please check my solution and point out my mistake.

total no. of selections possible= ¹⁵C₄

since there has to be at least 1 ball of each color,i first select 1 ball of each color,which can be done in ⁶C₁ * ⁴C₁ * ⁵C₁ ways.
now out of the remaining 12 balls i can select any ball,the condition that 1 ball of each color has to be selected will be satisfied everytime.
therefore total number of favorable cases = ⁶C₁ * ⁴C₁ * ⁵C₁ * ¹²C₁
so probability = (⁶C₁ * ⁴C₁ * ⁵C₁ * ¹²C₁ )/¹⁵C₄ which comes out to be 96/91 (not possible)
so where am i wrong?

_{the correct answer is 48/91}

there are two sets of numbers each consisting of 3 terms in A.P and the sum of each set is 15.the c.d of the first set is greater by 1 than the c.d of the second set,and the product of the first set is to the product of the second set as 7 to 8;find the numbers?

the number of terms in A.P.is even;the sum of odd terms is 24,of the even terms is 30;the last term exceeeds the first by 21/2.find the number of terms

the question is

A man can swim at a speed of 3kmph in stilll water. he wants to cross a 500 m wide river flowing at 2kmph. He keeps himself always at an angle of 120⁰ with the river flow.

a> Find the time taken to cross the river.

b> At what point on the opposite bank will he arrive?

My doubt occurs in the 2nd part of the question.
the answer of the second part is 96 m on the right side.
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here is my solution.

the time taken comes out to be 1/3\( \sqrt{3} \)

2nd part of the answer

step 1: diagram (click here)

step 2: click

step 3 : diagram

step 4: the displacement along the direction of Vsg is

           speed * time

           = \( \sqrt{19} \) * (1/3\( \sqrt{3} \))

           =  0.83 km.

step 5:  click here

The answer of my solution is wrong.

Can anyone please tell me where I am going wrong?

 

 

 

A thin biconvex thin lens is prepared from glass(refractive index=1.5), the two bounding surfaces having equal radii of 25 cm each.One of the surfaces is silvered from outside to make it reflecting.Where should an object be placed before this lens so that the image is formed on the object itself?I have some confusion about sign convention.So,please explain that in this question.

1)A magician during a show makes a glass lens with n=1.47and disappears in a trough of liquid.what is the refractive index of the fluid? 

 

I want to know the RS Nomenclature of Tartaric acid

I m getting confused with the priority group order
I know OH is the highest priority but then COOH group or the rest group with C2 carbon i.e. C(COOH)(OH)H is the 2nd highest priority grp.

1)Is resonance stabilisation in benzoic acid any different from that of an alkanoic acid, after the removal of H ion?

2)Can benzoic acid support negative charge on both the oxygens simultaneously?

3)Which of the two acids is more acidic?