Answer A is incorrect
A crest is just one point. It is not the distance between 2 crests.
B is incorrect
A trough is just 1 point. It is not the distance between 2 troughs.
C is incorrect.
the amplitude measures the height of a crest from the middle of the wave to the crest (or trough).
D is the correct answer. That is the distance between 2 crests or 2 troughs
The wave frequency is 2 Hz.
What is wave frequency ?
The number of waves that pass through a fixed point in a given amount of time is referred to as the wave frequency. The hertz is the SI unit for wave frequency (Hz).

where,

Given,


The waves frequency is 2 Hz.
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Answer:

Explanation:
The force of kinetic friction on the block is defined as:

Where
is the coefficient of kinetic friction between the block and the surface and N is the normal force, which is always perpendicular to the surface that the object contacts. So, according to the free body diagram of the block, we have:

Replacing this in the first equation and solving for
:

Answer:
The peak wavelength of the light it irradiates decreases
Explanation:
As the temperature of a blackbody increase, the peak wavelength of the light it radiates decreases, this follows Wien's Law.
A blackbody is an ideal substance that emits all frequencies of light and also has the ability to absorb them as well.
Wiens displacement law, explains that the position of the peak wavelength of the thermal radiation emitted by bodies can change with temperature, and as the temperature increases beyond a certain point, the wavelength begins to reduce. This often changes the colour of the light emitted from heated objects.