The force of gravity form the Sun will be stronger on a n object with more mass
That is more of a History of English question.
Looks like you simply substitute the length of the femur
Answer:

Explanation:
m = Mass of object = 
mg = Weight of object = 20 N
g = Acceleration due to gravity = 
v = Final velocity = 15 m/s
u = Initial velocity = 0
d = Distance moved by the object = 150 m
= Angle of slope = 
f = Force of friction
fd = Work done against friction
The force balance of the system is

The work done against friction is
.
For a constant-velocity object, the average and instantaneous are the same. So the answer is no. It's like taking a running average of a string of numbers that are all the same number. The average is always the sum of the numbers divided by how many have accumulated, which will always equate to the repeated number.