Answer:
The mechanical advantage of the system is 8
Explanation:
the mechanical advantage measures how much the system multiplies the input force to get the output.
In the given:
The input force (effort) is 20 Newton
The output force (load) is 160 Newton
This means that the mechanical advantage is:
mechanical advantage = load / effort = 160 / 20 = 8
Note that the mechanical advantage is unit-less (has no unit) since it is a ratio between two forces.
Hope this helps :)
Moving fan has rotational kinetic energy
Non moving fan has no energy since it is in rest
The heat released by the water when it cools down by a temperature difference

is

where
m=432 g is the mass of the water

is the specific heat capacity of water

is the decrease of temperature of the water
Plugging the numbers into the equation, we find

and this is the amount of heat released by the water.
The most exact answer is 78.4J also in this kind of options we can say answer "d"
A) 
The total energy of the system is equal to the maximum elastic potential energy, that is achieved when the displacement is equal to the amplitude (x=A):
(1)
where k is the spring constant.
The total energy, which is conserved, at any other point of the motion is the sum of elastic potential energy and kinetic energy:
(2)
where x is the displacement, m the mass, and v the speed.
We want to know the displacement x at which the elastic potential energy is 1/3 of the kinetic energy:

Using (2) we can rewrite this as

And using (1), we find

Substituting
into the last equation, we find the value of x:

B) 
In this case, the kinetic energy is 1/10 of the total energy:

Since we have

we can write

And so we find:
