C isotopes is the correct answer. Isotopes are variants of a particular chemical element which differ in neutron number, and consequently in nucleon number.All isotopes of a given element have the same number of protons but different numbers of neutrons in each atom.
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1) In the reference frame of one electron: 0.38c
To find the relative velocity of one electron with respect to the other, we must use the following formula:

where
u is the velocity of one electron
v is the velocity of the second electron
c is the speed of light
In this problem:
u = 0.2c
v = -0.2c (since the second electron is moving towards the first one, so in the opposite direction)
Substituting, we find:

2) In the reference frame of the laboratory: -0.2c and +0.2c
In this case, there is no calculation to be done. In fact, we are already given the speed of the two electrons; we are also told that they travel in opposite direction, so their velocities are
+0.2c
-0.2c
Answer:
C)the right cord pulls on the pulley with greater force than the left cord
Explanation:
As we can see the figure that B is connected to the right string while A is connected to the left string
Now force equation for B as it will move downwards is given as

similarly for block A which will move upwards we can write the equation as

now we know that pulley is also rotating so the tangential acceleration of the rope at the contact point with pulley must be same as that of acceleration of the blocks
so here pulley will rotate clockwise direction
So tension in the right string must be more than the left string
So correct answer will be
C)the right cord pulls on the pulley with greater force than the left cord
Answer:
Potential energy is energy that is stored – or conserved - in an object or substance. This stored energy is based on the position, arrangement or state of the object or substance. You can think of it as energy that has the 'potential' to do work.