Let's start with the concept of momentum. What is it? Linear momentum in physics is mathematically written as a product of mass and velocity of an object. Now let us suppose a body of mass m is moving in an inertial frame of reference with velocity v. Consider the fact that no external force is acting on the system. The momentum of this body is given by mv, where m is the mass and v is its velocity. In case of simple real world problems not delving into the realms of relativity, mass is a conserved quantity and it cannot be zero. Hence the velocity of the body must be zero and hence the momentum.
However, photons are considered to have a rest mass zero.
However note the point carefully "rest mass". A body in motion cannot have mass to be zero.
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Answer:

Explanation:
wavelength, λ = 2.5 m
speed, v = 13.8 m/s
Amplitude, A = 0.14 m
The general equation of the transverse harmonic wave which is travelling right is given by

where, Ф is phase
At t = 0, x = 0 , y = 0.14 m
0.14 = 0.14 Sin Ф
Ф = π/2
So, the equation is


Explanation:
In recent times of pandemic, robots can be use as replacement of labor in the industries. Mundane tasks can be programmed in their system so that they can used readily.
Drones can used delivery for essential goods and services, so that human interference can be least and the spread of virus can be curbed.
In a recent example, Argentina where aerial data has reportedly been used to accelerate the construction of emergency hospitals.
Answer:
It is used in MRI because it does not damage cells
Radio waves are used for space research because they have very long wavelengths
Explanation:
Many parts of the electromagnetic spectrum are applied in clinical diagnosis and treatment of illnesses. However, these highly ionizing radiation damage cells and its dosage must be carefully managed to avoid creating radiation related health problems for the patients.
Radio waves can be used in MRI without issues because the energy of the radiation is not sufficient to cause damage to cells but is sufficient to provide images for the sake of medical diagnosis.
Secondly, radio waves have long wavelength. This property is suitable for long range
communication. Hence it can be used in space research