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Atoms And Molecules

Question
CBSEENSC9006073
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 A ball is thrown vertically upwards with a velocity of 49 m/s. Calculate

(i) the maximum height to which it rises,

(ii) the total time it takes to return to the surface of the earth.

Solution

(i) Upward velocity is taken positive and acceleration due to gravity is taken negative, according tho the cartesian sign convention.
So, 
I n i t i a l space v e l o c i t y comma space straight u space equals space plus 49 space ms to the power of negative 1 end exponent A c c e l e r a t i o n space d u e space t o space g r a v i t y comma space straight g space equals negative 9.8 space ms to the power of negative 2 end exponent At space the space highest space point comma space straight v space equals space 0 U sin g space t h e space e q u a t i o n space o f space m o t i o n comma space space space space space space space space space space space space straight v squared minus straight u squared space equals space 2 gs therefore space space space 0 squared minus space 49 squared space equals space 2 left parenthesis negative 9.8 right parenthesis space cross times space straight s Maximum space height comma space straight s space equals space fraction numerator 49 space cross times space 49 over denominator 2 space cross times space 9.8 end fraction space equals space 122.5 space straight m. 
     
(ii) Let t be the time taken by the stone to reach the highest point. 
According to the equation,
                   v = u + gt
  therefore space space space space space 0 space equals space space space 49 space minus space 9.8 space cross times space straight t space space space space space space space space space space straight t space equals space fraction numerator 49 over denominator 9.8 end fraction space equals space 5 straight s
Since time of ascent = time of descent 
space Time space taken space by space the space stone space to space return space to space the space earth apostrophe straight s space surface space is comma space space space space space space space space space space space space space space space space 2 space straight t space equals space 2 space cross times space 5 space equals space 10 space straight s.



 

 

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Some More Questions From Atoms And Molecules Chapter

Write the chemical formulae of the following:

(a) Magnesium chloride
(b) Calcium oxide
(c) Copper nitrate 
(d) Aluminium chloride
(e) Calcium carbonate

Give the names of the elements in the following compounds.

(a) Quick lime
(b) Hydrogen bromide
(c) Baking powder 
(d) Potassium sulphate.

Calculate the molar mass of the following substances:

(a) Ethylene
(b) Sulphur molecule, S8
(c) Phosphorus molecule, P4
(d) Hydrochloric acid, HCl
(e) Nitric acid, HNO3.

What is the mass of:

(a) 1 mole of nitrogen atoms

(b) 4 moles of aluminium atoms

(c) 10 moles of sodium sulphite.

Convert into mole

(a) 12 gm of oxygen gas

(b) 20 gm of water

(c) 22 gm of carbon dioxide.

What is the mass of?

(a) 0.2 mole oxygen atoms.

(b) 0.5 mole of water molecules.

Calculate the number of molecules of sulphur (S8) present in 16 gm of solid sulphur.

Calculate the number of aluminium ions present in 0.56 gm of aluminium oxide.

Explain law of conservation of mass.

50 g of 10% lead nitrate is mixed with 50 g of 10% sodium chloride in a closed vessel. After the reaction has taken place, it was found that 6.83 g of lead chloride was precipitated. Besides, the reaction mixture contained 90 g water and sodium nitrate. Calculate the amount of sodium nitrate formed.

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