# National Science Olympiad Model Paper 1 Questions and Answers Part 4

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14. An observer stands at a distance of 850 m from a cliff and fires a gun. After what time gap will he hear the echo, if sound travels at a speed at 350 ms − 1 in air?

A) 20s

B) 1.42s

C) 40s

D) 2.42s

Answer: A

Explanation:

15. The pressure of a gas contained in a cylinder with a movable piston is 400 Pa. The area of the piston is 0.5 m2. Calculate the force that is exerted on the piston.

A) 150N

B) 200N

C) 800N

D) 100N

Answer: A

Explanation

Pressure is defined as force per unit area or P = F/A

We multiply both sides of the equation by the area to solve for the force as F = P A

F = (300 Pa) (0.5 m2)

F = 150 Pa = 150 (N/m2) /

F = 150 N

Q. 16. The given table shows the speed for a ball bowled by a bowler in an over.

 Balls 1 2 3 4 5 6 Bowling speed (m s – 1) 45 44 48 42 36 40

If the cricket pitch is about 22 m long, then the average time taken by the ball to reach batsman after the bowler release the ball is.

A. 0.46

B. 0.48

C. 0.51

D. 0.52

Answer: C

Explanation:

As per the table, the average speed is .

It means it covers 41.66 in one second. Now, the pitch is 22 m. Hence, to calculate the time taken for the ball to cover 20m will be =

Q. 17. According to the Dalton՚s atomic theory all matter is made of tiny particles called ________.

A) Molecules

B) Moles

C) Atoms

D) Elements

Answer: C

Explanation:

Dalton՚s atomic theory proposed that all matter was composed of atoms, indivisible and indestructible building blocks.

While all atoms of an element were identical, different elements had atoms of differing size and mass.

Q. 18. Calculate the number of Sulphur molecules in a 300 g sample of Sulphur [S8] .

A) 7.7 × 1020molecules

B) 7.05 × 1023molecules

C) 5.07 × 1023molecules

D) 6.023 × 1023molecules

Answer: B

Explanation:

The molecules formula of Sulphur is given to be S8 (it Contains 8 atoms of Sulphur) . So , the molecular mass of Sulphur molecule is 32 × 8 = 256 u. This means that 1 mole of Sulphur molecules is equal to 256 grams.

Now, 256 g of Sulphur = 1 mole of Sulphur molecules

1 g = 1/256 mole

So, 300g = moles

And we know that 1 mole = atoms

So, 300 g has = = atoms

Q. 19. Observe the given chart answer the question.

The value of a and b is

A) a = multiply by 22.4 L, b = multiply by 22.4 L

B) a = multiply by 22.4 L, b = divide by 22.4 L

C) a = divide by 22.4 L, b = divide by 22.4 L

D) a = divide by 22.4 L, b = multiply by 22.4 L

Answer: B

Explanation:

Volume of gas at STP = No. of moles × 22.4 L which is the value of (a)

No. of moles = Volume of gas at STP ÷ 22.4 L which is the value of (b)

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