The sentence can be completed as follows:
The wavelength of an electromagnetic waves is the spatial distance between two successive troughs.
Note that the wavelength of a wave can also measured as the spatial distance between two successive crests of the wave. Also note that the second part of the sentence ("also known as the period") is not true, because period is another thing (in fact, the period is the time interval between two successive troughs).
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There are 5,280 feet in 1 mile.
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Incomplete question as the unit of volume is not written correctly.So the complete question is here:
A straightforward method of finding the density of an object is to measure its mass and then measure its volume by submerging it in a graduated cylinder. What is the density of a 240-g rock that displaces 89.0 cm³?
Answer:

Explanation:
Given data
Mass m=240g
Volume V=89.0 cm³
To find
Density d
Solution
If rock displaces 89.0 cm³ of water means volume of rock is also 89cm³
So

Answer:
6.23x10^6Pa
Explanation:
Data obtained from the question include:
F (force) = 490N
r (radius) = 0.005m
A (area of the circlular heel) =?
P (pressure) =.?
First, we'll begin by calculating the area of the circlular heel. This is illustrated below:
Area of circle = πr^2
Area = 22/7 x (0.00)^2
Area = 7.86x10^-5m^2
Pressure is simply force per unit area. It represented mathematically as
Pressure = Force /Area
Pressure = 490/7.86x10^-5
Pressure = 6.23x10^6N/m2
Recall: 1N/m2 = 1Pa
Therefore, 6.23x10^6N/m2 = 6.23x10^6Pa
Therefore, the woman exert a pressure of 6.23x10^6Pa on the floor