Answer:
when the ground is very hot and the air is cool.
Explanation:
The hot earth warms a layer of air right above the ground. Light is refracted as it passes through the cool air and onto the hot air sheet (bent). A coating of very warm air near the earth bends the light from the sky almost into a U-shaped bend.
The charge of the object must be 
Answer: Option C
<u>Explanation:</u>
Suppose an electric charge can be represented by the symbol Q. This electric charge generates an electric field; Because Q is the source of the electric field, we call this as source charge. The electric field strength of the source charge can be measured with any other charge anywhere in the area. The test charges used to test the field strength.
Its quantity indicated by the symbol q. In the electric field, q exerts an electric, either attractive or repulsive force. As usual, this force is indicated by the symbol F. The electric field’s magnitude is simply defined as the force per charge (q) on Q.

Here, given E = 4500 N/C and F = 0.05 N.
We need to find charge of the object (q)
By substituting the given values, we get

Answer:
Approximately
, assuming friction between the vehicle and the ground is negligible.
Explanation:
Let
denote the mass of the vehicle. Let
denote the initial velocity of the vehicle. Let
denote the spring constant (needs to be found.) Let
denote the maximum displacement of the spring.
Convert velocity of the vehicle to standard units (meters per second):
.
Initial kinetic energy (
) of the vehicle:
.
When the vehicle is brought to a rest, the elastic potential energy (
) stored in the spring would be:
.
By the conservation of energy, if the friction between the vehicle and the ground is negligible, the initial
of the vehicle should be equal to the
of the vehicle. In other words:
.
Rearrange this equation to find an expression for
, the spring constant:
.
Substitute in the given values
,
, and
:

Answer:
a) 2 m/s
b) i) 
ii) 
Explanation:
The function for distance is 
We know that:
Velocity = 
Acceleration = 
To find speed at time t = 0, we derivate the distance function:

Substitute t = 0 in velocity function:

Velocity at t = 0 will be 2 m/s.
To find the function for Kinetic Energy of the box at any time, t.

We know that 


Answer:
The electric field strength needed is 4 x 10⁵ N/C
Explanation:
Given;
magnitude of magnetic field, B = 0.1 T
velocity of the charge, v = 4 x 10⁶ m/s
The velocity of the charge when there is a balance in the magnetic and electric force is given by;

where;
v is the velocity of the charge
E is the electric field strength
B is the magnetic field strength
The electric field strength needed is calculated as;
E = vB
E = 4 x 10⁶ x 0.1
E = 4 x 10⁵ N/C
Therefore, the electric field strength needed is 4 x 10⁵ N/C