Explanation:
Hydrogen is used as a fuel because it has a high calorific value per molecule when burned in air and also burns explosively. When burned in air, it reacts with oxygen to produce water which is safe for the environment. This same property of hydrogen of high explosiveness makes it difficult to store safely.
Hydrogen can be produced through the electrolysis of water. However this is high energy consuming. The most common method is called steam-methane reforming. Methane from hydrocarbon is mixed with steam under high pressure and reacts to produce hydrogen and carbon monoxide.
Diesel and petrol and other petroleum products when burned produce carbon dioxide which is a greenhouse gas. Greenhouse gases when increasing in the atmosphere, cause greenhouse effect that results in global warming.
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Answer:
f' = 2 f
Explanation:
The frequency of the pendulum that swings in simple harmonic motion is given by :

Where
l is the length of pendulum
g is the acceleration due to gravity
If the length of the thread is increased by a factor of 4, such that, l' = 4 l, let f' is the new frequency such that,



f' = 2 f
So, the new frequency of the pendulum will become 2 time of initial frequency. Hence, the correct option is (b) "2f"
Answer:

Explanation:
Our values are


We can find the time through



The expression for the distance between the Earth and the spaceship is as follow:

Where c is Light speed, and t our previous time.


Therefore the distance between the Eath and the Spaceship is
m