Friction occurs when the surfaces and heat of two surfaces grind against each other.
I think these are the answers
Answer:
600m
Explanation:
30×20 at a constant speed is 600m.
Answer:
a)
, b) 
Explanation:
a) The magnetic force experimented by a particle has the following vectorial form:

The charge of the electron is equal to
. Then, cross product can be solved by using determinants:

The magnetic force is:

b) The charge of the proton is equal to
. Then, cross product has the following determinant:

The magnetic force is:

Combine all of the x's on one side of the equation and then finish the problem!
The pressure of the air inside the balloon is higher than outside, and when you pop the balloon, the high pressure air expands quickly and makes a popping sound.