Answer:
B is correct. Electrons are added to the rod.
Explanation:
Because the fur lose electrons to the rode and because positively charged while the rod because negative
Answer:
8.9
Explanation:
We can start by calculating the initial elastic potential energy of the spring. This is given by:
(1)
where
k = 35.0 N/m is the initial spring constant
x = 0.375 m is the compression of the spring
Solving the equation,

Later, the professor told the student that he needs an elastic potential energy of
U' = 22.0 J
to achieve his goal. Assuming that the compression of the spring will remain the same, this means that we can calculate the new spring constant that is needed to achieve this energy, by solving eq.(1) for k:

Therefore, Tom needs to increase the spring constant by a factor:

I electromagnets, the magnetic field is turned off when there is no induced current. So, electromagnets act as magnets only when current is induced in an insulated wire wrapped around a material mage of ferromagnetic material such as iron core rotating in a magnetic field.
So, option D is the correct one.
If you wanna know more about electromagnets, write down in comments {:
Answer:
200J
Explanation:
200J is 100%, 10% of 200J would be 20J
a)
, 
The work done by the student in each trial is equal to the gravitational potential energy gained by the student:

where
m = 68 kg is the mass of the student
g = 9.8 m/s^2 is the acceleration of gravity
is the gain in height of the student
For the first student,
, so the work done is

The second student runs up to the same height (3.5 m), so the work done by the second student is the same:

2)
, 
The power exerted by each student is given by

where
W is the work done
t is the time taken
For the first student,
and
, so the power exerted is

For the second student,
and
, so the power exerted is
