The thermal energy is where the work of friction comes from. That is what stops it eventually. In this case a counter force of 10N is applied over the distance of 30.0m. The energy is given by Force*Distance. Here this is 300J. This friction work is the thermal energy.
We use the equation of motion,

Here, S is the height, u is initial velocity and a is acceleration.
Given,
As acorn falls from tree, therefore we take the value of
and initial velocity
.
Substituting these values in equation of motion,

Thus, the time taken by the acorn to fall 20 feet ( 6.096 m ) is 1.12 s.
Answer: Mass of the planet, M= 8.53 x 10^8kg
Explanation:
Given Radius = 2.0 x 106m
Period T = 7h 11m
Using the third law of kepler's equation which states that the square of the orbital period of any planet is proportional to the cube of the semi-major axis of its orbit.
This is represented by the equation
T^2 = ( 4π^2/GM) R^3
Where T is the period in seconds
T = (7h x 60m + 11m)(60 sec)
= 25860 sec
G represents the gravitational constant
= 6.6 x 10^-11 N.m^2/kg^2 and M is the mass of the planet
Making M the subject of the formula,
M = (4π^2/G)*R^3/T^2
M = (4π^2/ 6.6 x10^-11)*(2×106m)^3(25860s)^2
Therefore Mass of the planet, M= 8.53 x 10^8kg
Answer:
Order of maximum transmission of the polarizer is A, C and B.
Solution:
As per the question:
For the first polarizer, the angle is quite insignificant:
(A)
:
The light intensity after passing through the first polarizer is
and this intensity does not depend on the angle of the polarizer.
Consider
with the vertical, the intensity is given by:

(B)
:
Suppose the second polarizer is
with the vertical.
Now, intensity through the second polarizer:


Now, if we consider the second polarizer to be
,

(C)
:
Now,
Intensity through the third polarizer, if it is
with the vertical:

