Answer:
6. A
7. C
8. B
9. The average speed is the distance (a scalar quantity) per time ratio. Speed is ignorant of direction. The average velocity is the displacement or position change (a vector quantity) per time ratio.
By the right hand rule the magnetic force on the charge acts up
This type of a problem can be solved by considering energy transformations. Initially, the spring is compressed, thus having stored something called an elastic potential energy. This energy is proportional to the square of the spring displacement d from its normal (neutral position) and the spring constant k:

So, this spring is storing almost 12 Joules of potential energy. This energy is ready to be transformed into the kinetic energy when the masses are released. There are two 0.2kg masses that will be moving away from each other, their total kinetic energy after the release equaling the elastic energy prior to the release (no losses, since there is no friction to be reckoned with).
The kinetic energy of a mass m moving with a velocity v is given by:

And we know that the energies are conserved, so the two kinetic energies will equal the elastic potential one:

From this we can determine the speed of the mass:

The speed will be 7.74m/s in in one direction (+), and same magnitude in the opposite direction (-).
Tsunami and under water volcano
Here is the energy that is left after the quantity of energy is transformed: 750 j of electrical energy is changed into 400 j of kinetic or mechanical energy, which is then turned into 0.32 j of efficient energy.
To run the fan, electrical energy is utilized.
Here, under the specified circumstances, 750 J of electrical energy is utilized to operate the fan, which is transformed into 400 J of kinetic energy. As a result, 350 J of energy is wasted due to various frictional and resistive losses.
Therefore, we may conclude that only 400 J of the 750 J available energy is used to power the fan, with the remaining energy being wasted as a result of friction.
Additionally, we can state that this fan's effectiveness will be
n = Useful ÷ Total
n = 400 ÷ 750
n = 8 ÷ 25
n = 0.32
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