The correct answer, is Option C, I hope this helps :)
<h2>
Answer:</h2>
(a) 10.00V
(b) 0.5V
<h2>
Explanation:</h2>
(a) The power(P) supplied by a resistor of resistance (R) when a voltage(V) is passed across is given by;
P = V² / R ------------------(i)
From the question;
P = 5.00W
R = 20.00Ω
Substitute these values into equation (i) as follows;
5.00 = V² / 20.00
V² = 5.00 x 20.00
V² = 100.00
V = 
Solve for V;
V = 10.00V
Therefore, the maximum voltage that can be applied without harming the resistor is 10.00V
(b) By Ohm's law the current (I) flowing through a resistor of resistance (R) when a voltage (V) is applied is given by;
V = I x R
=> I = V / R ----------------(ii)
Substitute the values of V and R into equation (ii) as follows;
I = 10.00 / 20.00
I = 0.5A
Therefore, the current through the resistor is 0.5A
Answer:

Explanation:
Assuming that cars 4 and 5 have same mass so that the momentum
P=mv where m is mass and v is velocity hence
Momentum=0+2mv+3mv=5mv
The final mass is 2m+3m=5m
From aw of conservation of momentum
hence 
Therefore, the speed is 
The ratio of the speed of light v in a medium to the speed of light in a vacuum c is called its Refractive Index n
v/c=n
Different substances have different Refractive Indices (plural of Index). Values are always bigger than 1.
Refractive index of water is 1.33
Refractive index of glass is about 1.4