Answer:
0.82 m/s
Explanation:
From the law of conservation of momentum,
Total momentum = Final momentum.
mu+m'u' = V(m+m')......................... equation 1
Where m = mass of Lillian, u = initial velocity of Lillian before she catches the dog, m' = mass of the dog, u' = initial velocity of the dog, V = velocity of Lillian and the dog.
make V the subject of the equation,
V = (mu+m'u')/(m+m')................ Equation 2
Given: m = 40 kg, m' = 15 kg, u = 0 m/s (Lillian was standing at rest), u' = 3.0 m/s.
Substitute into equation 2
V = (40×0+15×3)/(40+15)
V = (0+45)/55
V = 45/55
V = 0.82 m/s
An object will remain at rest or in uniform motion until acted upon by an external unbalanced source. Ex) a ball remaining still until kicked by a foot.
To solve this problem it is necessary to apply the definition of Young's Module which states that

Where,
F = Force
A = Cross sectional Area
L = Length
= Initial Length
We need to find the ratio between the two values when the another values are constant, that is


Re-arrange to find 


Therefore the bone stretch around 
The power of the antenna is

and since the power is the emitted energy divided by the time, the energy emitted per second is

The frequency of the emitted photons is

So the energy of a single photon is

Therefore, to find the number of emitted photons per second, we should divide the total energy emitted by the antenna in 1 second by the energy of a single photon: