A) 
The total energy of the system is equal to the maximum elastic potential energy, that is achieved when the displacement is equal to the amplitude (x=A):
(1)
where k is the spring constant.
The total energy, which is conserved, at any other point of the motion is the sum of elastic potential energy and kinetic energy:
(2)
where x is the displacement, m the mass, and v the speed.
We want to know the displacement x at which the elastic potential energy is 1/3 of the kinetic energy:
Using (2) we can rewrite this as
And using (1), we find
Substituting 
into the last equation, we find the value of x:
B) 
In this case, the kinetic energy is 1/10 of the total energy:
Since we have
we can write
And so we find:
It is actually caused by the environment, so its false. :)
Answer:
Explanation:
From A to B
distance traveled with velocity 
in time 
from B to C
distance traveled is 0.5 d with 
and 
velocity for half-half time
divide 1 and 2 we get
Now average velocity is given by
taking common
Explanation:
It is given that,
Spring constant of the spring, k = 15 N/m
Amplitude of the oscillation, A = 7.5 cm = 0.075 m
Number of oscillations, N = 31
Time, t = 15 s
(a) Let m is the mass of the ball. The frequency of oscillation of the spring is given by :
Total number of oscillation per unit time is called frequency of oscillation. Here, 
m = 0.0895 kg
or
m = 89 g
(b) The maximum speed of the ball that is given by :
Hence, this is the required solution.
