1) 
When both the electric field and the magnetic field are acting on the electron normal to the beam and normal to each other, the electric force and the magnetic force on the electron have opposite directions: in order to produce no deflection on the electron beam, the two forces must be equal in magnitude
where
q is the electron charge
E is the magnitude of the electric field
v is the electron speed
B is the magnitude of the magnetic field
Solving the formula for v, we find
2) 4.1 mm
When the electric field is removed, only the magnetic force acts on the electron, providing the centripetal force that keeps the electron in a circular path:
where m is the mass of the electron and r is the radius of the trajectory. Solving the formula for r, we find
3) 
The speed of the electron in the circular trajectory is equal to the ratio between the circumference of the orbit, 
, and the period, T:
Solving the equation for T and using the results found in 1) and 2), we find the period of the orbit:
When the surface of the comb rubs on your hair, the comb is electrically charged. When the comb comes close to the paper, the charge on the comb causes charge separation on the paper bits. Since paper is neutral, positive and negative charges are equivalent. The charge on the comb charges the area of the bit of paper nearest the comb to the opposite. Thus, the bits of paper become attracted to the comb.
<span>The power ratings of several motors are listed in the table.
Motor Power
Brandy X 7,460
Brandy Y 7,650
Brandy Z 7,580
An advertising agency writes marketing material for a new motor (Brand W) that has a power rating of 7,640 W. Which statement comparing the motors can they truthfully use?
I believe the answer is </span><span>Brand W motor does more work each second than Brand X or Brand Z.</span>
Answer:
The value is 
Explanation:
From the question we are told that
The speed of the marathon runner is 
The distance from the distance from the finish is 
The speed of the bird is 
Generally the time taken for the runner to reach the finish is mathematically represented as
So the distance covered by the bird is
Answer:
The minimum coefficient of static friction is: 0.5
Explanation:
We need to represent the forces of the display board (see attached) as free body diagram. Then we need to remember that the display board is in translational and rotational equilibrium, so we can sum of forces acting to x axis and y axis getting from the sum of forces acting at x axis as:
, we need to remember that friction force is: 
where u is the friction coefficient and N is the normal force at the surfaces in contact so replacing we get:
, so 
this is the equation (1). Now we need to sum forces at y axis:
, so 
. For doing the rotational equilibrium, we need to choose the ground as the point about which to take the torques: 
, this is for convenience because two forces passes through the point, as a result they don't have moment arm so we get:
, so
, this is the equation (2). Assuming that the board has a height as: L and remember that was cutting it in half, both sides have as longitude:L/2 and applying trigonometric identities, we can find as:
and
(see attached), and replacing this at equation (2), we get:
and solving to Nboard we get
. Now we can replace those results at equation (1), Now we can find the friction coefficient as:
.
