The correct answer is 1 and 4.
Burning of fossil fuels releases harmful gases to the atmosphere which leads to climate change. Burning of hydrogen gas releases water which has no negative effect on climate.
Burning of both fossil fuels and hydrogen takes place inside expensive fuel cells.
Fossil fuels are widely available and easy to locate whereas hydrogen is available in the combined form with other elements. Hydrogen are not found in pure form on earth.
Fossil fuels are non-renewable source of energy which means they cannot be replaced in short time.
Answer: There is not work done at the door because the door did not move.
Explanation: Work is defined as the movement done by a force.
So if you move to apply a force F in an object and you move it a distance D, the work applied on the object is
W = F*D
In this case, the secret agent pushes against the door, so there is a force, but the agent does not move the door, so D = 0, so there is no motion of the door, which implies that there is no work done at the door.
Answer:
Final velocity v = 8.944 m/sec
Explanation:
We have given distance S = 40 meters
Time t = 10 sec
As it starts from rest so initial velocity u = 0
From second equation of motion 
Now from first equation of motion 
, here v is final velocity, u is initial velocity, a is acceleration and t is time
So 
Answer:
Precipitation is the formation of a solid from a solution. It is necessary to centrifuge the precipitate to exert sufficient forces of gravity to bring the solid particles in the solution to come together and settle
Explanation:
When you centrifuge precipitate it enables the nucleation to form.
Centrifuging the precipitate helps in determining whether a certain element is present in a solution or not.
Answer:
The first graph
Explanation:
Graph A shows acceleration.
