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Relative position of a helicopter

If a helicopter takes off from a point on earth.(at certain altitude) and its still at that point in air.After certain time interval the observer whose position was same as that of helicopter’s take off point will see the helicopter right above him.
The question arises is that how it is possible if earth is rotating hence the observer is also, but the helicopter is in air.How is it possible?
Thanks…

Explain IMPULSE in simple terms

Impulse is the effect of a force and is measured as the change in momentum produced.

The same effect, that is the same change in momentum can be produced by a large force acting for a short interval of time, a small force acting for a large interval of time or a moderate force acting for a moderate interval of time.

In all these cases the impulse will be the same as the change in momentum will be the same.

Big Bang and the conservation of Mass

“During the big bang it is supposed that the small particles expanded in a very very small interval of time and there was nothing before that. If it is so, then how can it in be good agreement with law of conservation of mass?”

Ans:

After the Big Bang, the universe expanded rapidly. The big bang theory is not a theory which is completely resolved. There are many questions to be answered.

Further, mass alone is not conserved, it is mass+energy  which is conserved.

Energy can be converted into matter and vice versa. ($E=mc^{2}$)

Dark Energy and Dark Matter are two widely discussed concepts in association with the Big Bang. These correspond to the mass (matter) and energy which we cannot account for by calculations and theory.

Further, BIGBANG is not the only possible cause of the Birth of Universe. There are many other possibilities.

Big Bang theory originated after the discovery that the universe is expanding. SO if we think in reverse direction, we can imagine that the entire universe was confined to an infinitesimally small (Compared to the present size of the universe) space. This idea started the theoritization of the Big Bang.

(Comments and better answers are expected from visitors and experts visiting the site)

Numericals from Kinematics

Posted By – Abdul Hameed

1. During the first 18 minutes of a 1.0-hour trip, a car has an average speed of 11 m/s. What must the average speed of the car be during the last 42 minutes of the trip be if the car is to have an average speed of 21 m/s for the entire trip?
2. An elevator is moving upward with a speed of 11 m/s. Three seconds later, the elevator is still moving upward, but its speed has been reduced to 5.0 m/s. What is the average acceleration of the elevator during the 3.0 s interval?
3. A turtle takes 3.5 minutes to walk 18 m toward the south along a deserted highway. A truck driver stops and picks up the turtle. The driver takes the turtle to a town 1.1 km to the north with an average speed of 12 m/s. What is the magnitude of the average velocity of the turtle for its entire journey?