The work done to pull the sister back on the swing is equal to the increase in potential energy of the sister:

(1)
where m is the sister's mass, g is the gravitational acceleration and

is the increase in altitude of the sister with respect to its initial position.
By calling

the angle of the chain with respect to the vertical, the increase in altitude is given by

(2)
where L is the length of the chain.
Putting (2) inside (1), we find

from which we can find the mass of the sister:
Answer:
The moment of inertia is 
Explanation:
From the question we are told that
The frequency is 
The mass of the pendulum is 
The location of the pivot from the center is 
Generally the period of the simple harmonic motion is mathematically represented as

Where I is the moment of inertia about the pivot point , so making I the subject of the formula it
=> ![I = [ \frac{T}{2 \pi } ]^2 * m* g * d](https://tex.z-dn.net/?f=I%20%3D%20%20%5B%20%5Cfrac%7BT%7D%7B2%20%5Cpi%20%7D%20%5D%5E2%20%2A%20%20m%2A%20%20g%20%2A%20d)
But the period of this simple harmonic motion can also be represented mathematically as

substituting values


So
![I = [ \frac{2.174}{2 * 3.142 } ]^2 * 2.40* 9.8 * 0.380](https://tex.z-dn.net/?f=I%20%3D%20%20%5B%20%5Cfrac%7B2.174%7D%7B2%20%2A%203.142%20%7D%20%5D%5E2%20%2A%20%20%202.40%2A%20%209.8%20%2A%200.380)

Answer:
If it is not an object in motion, all forces are balanced.
<span>step 1: energy required to heat coffee
E = m Cp dT
E = energy to heat coffee
m = mass coffee = 225 mL x (0.997 g / mL) = 224g
Cp = heat capacity of coffee = 4.184 J / gK
dT = change in temp of coffee = 62.0 - 25.0 C = 37.0 C
E = (224 g) x (4.184 J / gK) x (37.0 C) = 3.46x10^4 J
step2: find energy of a single photon of the radiation
E = hc / λ
E = energy of the photon
h = planck's constant = 6.626x10^-34 J s
c = speed of light = 3.00x10^8 m/s
λ = wavelength = 11.2 cm = 11.2 cm x (1m / 100 cm) = 0.112 m
E = (6.626x10^-34 J s) x (3.00x10^8 m/s) / (0.112 m) = 1.77x10^-16 J
step3: Number of photons
3.46x10^4 J x ( 1 photon / 1.77x10^-16 J) = 1.95x10^20 photons</span>