20.4 years is 20.4/10.2 = 2 half-life cycles, which means a quarter of the starting mass or 15.2 g will remain after this time.
Density = mass / volume ;
1 Cubic Centimeter = 0,000001 Cubic Meter
8 cm^3 = 0.000008 m^3
12,9 g = 0,0129 kg
The density is 0,0129 kg/ 0,000008 m^3 = <span><u>1612,5 kg/m^3</u> </span>
Answer:
Terminal speed, v = 6901.07 m/s
Explanation:
It is given that,
Mass of the horizontal bar, m = 30 g = 0.03 kg
Length of the bar, l = 13 cm = 0.13 m
Magnetic field, 
Resistance, R = 1.2 ohms
We need to find the terminal speed oat which the bar falls. When terminal speed is reached,
Force of gravity = magnetic force
..................(1)
i is the current flowing
l is the length of the rod
Due to the motion in rods, an emf is induced in the coil which is given by :
, v is the speed of the bar


Equation (1) becomes,



v = 6901.07 m/s
So, the terminal speed at which the bar falls is 6901.07 m/s. Hence, this is the required solution.
The answer is a Viscosity because it describes the internal friction of a moving liquid
Its b, energy waiting to be used