I uploaded the answer to a file hosting. Here's link:
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Answer:
a)
& 
b) 
c) 
Explanation:
Given:
mass of the book, 
combined mass of the student and the skateboard, 
initial velocity of the book, 
angle of projection of the book from the horizontal, 
a)
velocity of the student before throwing the book:
Since the student is initially at rest and no net force acts on the student so it remains in rest according to the Newton's first law of motion.

where:
initial velocity of the student
velocity of the student after throwing the book:
Since the student applies a force on the book while throwing it and the student standing on the skate will an elastic collision like situation on throwing the book.

where:
final velcotiy of the student after throwing the book
b)



c)
Since there is no movement of the student in the vertical direction, so the total momentum transfer to the earth will be equal to the momentum of the book in vertical direction.



Explanation:
Electromagnetic waves are the waves which are created as the result of the electrical waves which are perpendicular to each other and also perpendicular to the direction of propagation.
Electromagnetic spectrum is range of the frequencies and their respective wavelengths of the various type of the electromagnetic radiation.
In order of the increasing frequency and the photon energy and the decreasing wavelength the spectrum are:
radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays.
The energy of the radio waves photons is the lowest of all the other waves in the electromagnetic spectrum.
Also, 
Where,
h is Plank's constant having value 
Thus, energy is directly proportional to the frequency. The radio waves have the lowest frequency.
Hi there!
Impulse = Change in momentum
I = Δp = mΔv = m(vf - vi)
Where:
m = mass of object (kg)
vf = final velocity (m/s)
vi = initial velocity (m/s)
Begin by converting grams to kilograms:
1 kg = 1000g ⇒ 145g = .145kg
Now, plug in the given values. Remember to assign directions since velocity is a vector. Let the initial direction be positive and the opposite be negative.
I = (.145)(-20 - 17) = -5.365 Ns
The magnitude is the absolute value, so:
|-5.365| = 5.365 Ns