Answer: A. X-rays
Explanation:
X-rays have the shortest wavelength and the highest energy of all of the options given.
Answer: 1.95
Explanation:
You should start off from the decay formula and solve for τ:


Apply inverse logarithmic function:

The final form will be:

Inputing values for I, IO, and t:
If one of two interacting charges is doubled, the force between the charges will double.
Explanation:
The force between two charges is given by Coulomb's law

K=constant= 9 x 10⁹ N m²/C²
q1= charge on first particle
q2= charge on second particle
r= distance between the two charges
Now if the first charge is doubled,
we get 
F'= 2 F
Thus the force gets doubled.
Answer:
The block's mass should be 
Explanation:
Given:
Cart with mass 
From the conservation of energy before mass is added,

Where
amplitude of spring mass system,
spring constant

Now new mass
is added to the system,


Here, given in question frequency is reduced to half so we can write,

Where
frequency of system before mass is added,
frequency of system after mass is added.




Therefore, the block's mass should be 
Answer:
it must be helical motion in which the charge particle will move uniformly along z axis and simultaneously it will move in circular path in xy plane.
Explanation:
Magnetic field is along z axis while velocity is in x-z plane
so we will have

so here we can say

so we will have

so here the net force on the charge is perpendicular to its x directional velocity along - Y direction
So due to this component of motion it will move along a circle while other component of the motion will remain uniform always
So here it is combination of two parts
1) Uniform circular motion
2) Uniform motion
So we can say that it must be helical motion in which the charge particle will move uniformly along z axis and simultaneously it will move in circular path in xy plane.