If the object, ends up with a positive charge, then it is missing electrons. if it is missing electrons, then it must have been removed form the object during the rubbing process.
The force applied to the lever is 400 N, because the force applied by the lever (800 N) divided by the mechanical advantage of the lever (4) equals
400 N.
(800/4) = 200
Explanation:
Given that,
Length of each rod, L = 15 m
Area of cross section of the rod, 
Young's modulus for steel, 
Total weight of two people, F = 1900 N
We need to find the stretching in the rod when the ride is at rest. The formula of Young's modulus of a material is given by :

Here,
is the stretching in the rod

So, the rod will stretched to 
Answer:
(c) 6.91x10^14 Hz
Explanation:
Find the level energy of n=2 and n=5, using the formula:

where 


To jump from n=2 to n=5 the electron absorbs a photon with energy equal to
, using the next formula to find specific wavelength
to that energy

Where
is the speed of light (
) and
is Planck's constant (
). Solve for
:

The frequency of this wavelength is calculated with this formula:


The awnser is C. Breast stroke Hope this helps :)