Answer: 
Explanation:
The equation to calculate the center of mass 
of a particle system is:
In this case we can arrange for one dimension, assuming the geometric center of the Earth and the ladder are on a line, and assuming original center of mass located at the Earth's geometric center:
Where:
is the mass of the Earth
is the mass of 1 billion people
is the radius of the Earth
is the distance between the center of the Earth and the position of the people (2 m above the Earth's surface)
This is the displacement of Earth's center of mass from the original center.
Answer:
Explanation: forces can cause an object to rotate and the turning effect of the force is called a moment. If a resultant force acts on an object about a fixed turning point it will cause the object to rotate e.g. turning a with a spanner, applying a screwdriver, opening a door fixed on
Answer:
Minimum time = 1.95x10^-4 s
Number of pulses = 5128.21 pulses/s
Explanation:
We have the speed of sound waves through human tissue with a value of 1540 m/s, to calculate the time it takes for the pulse to travel a distance of 30 cm (since the pulse will first travel a distance of 15 cm and then it will return another 15 cm to be detected by the equipment), therefore, the time between the two pulses will be equal to:
tminimum = 0.30 m/1540 m/s = 1.95x10^-4 s
To calculate the number of pulses, one second must be divided over the minimum time between the two pulses, as follows:
npulses = 1 s/1.95x10^-4 s = 5128.21 pulses/s
