Answer:
Free-fall is defined as the movement where the only force acting on an object is the gravitational force.
By the second Newton's law, we have that:
F = m*a
Where F = Force, m = mass, a = acceleration.
We can write this as:
a = F/m
And the gravitational force can be written as:
F = (G*M/r^2)*m
Where G is the gravitational constant, M is the mass of the Earth in this case, and r is the distance between both objects (the center of the Earth and the free-falling object)
As the radius of the Earth is really big, the term inside the parentheses is almost constant in the region of interest, then we can write:
G*M/r^2 ≈ g
And the gravitational force is:
F = g*m
And by the second Newton's law we had:
a = F/m = (g*m)/m = g
a = g
Then the acceleration does not depend on the mass of the object.
Then the thing that is common among the free-falling objects is the vertical acceleration.
By applying force on the object. Force changes the direction of motion of the object. For example : a soccer player control the motion of a soccer ball by applying a force. It will change the ball's direction not its speed.
Transvere wave because the direction which the particles are being displaced
Answer:
The time interval is 22.76 hr.
Explanation:
Given that,
Time = 30 hrs
Speed = 0.74c
We need to calculate the time interval measured in earth frame
Using formula of time dilation
Where, 
= time interval measured in earth frame
=proper time interval
Put the value into the formula
We need to calculate the proper time interval when the velocity is 0.86c
Using formula of time dilation
Hence, The time interval is 22.76 hr.
