The category of galaxy which does not have a distinctive shape is D. an irregular galaxy.
A spiral galaxy has a spiral shape, an elliptical galaxy has an elliptical shape, and a barred-spiral galaxy has a barred-spiral shape. The only galaxy type which does not have a constant shape is an irregular galaxy.
Answer:

Explanation:
P = Power = 50 kW
n = Number of photons per second
h = Planck's constant = 
= Frequency = 781 kHz
r = Distance at which the photon intensity is i = 1 photon/m²
Power is given by

Photon intensity is given by

The distance is 
Gravity is the force that attracts all matter to each other.
Explanation:
Sir Isaac Newton discovered Gravity when he saw a falling apple while thinking about the forces of nature.
Gravity is a fundamental force that causes objects to have weight. Gravity acts on all matter and is a function of both mass and distance. Each object attracts every other object with a force that is proportional to the product of their masses and inversely proportional to the square of the distance between them. The force of attraction is, however, negligible between most objects because of their small size.
Gravitational force is given as:

Where G is gravitational constant and is equal to 6.674×10−11 m³⋅kg⁻¹⋅s⁻²
m₁ and m₂ are the masses of the two objects.
r is the distance between the two objects.
The gravity is what makes an apple fall on the ground and gravity is the force that keeps us on the ground.
Keywords: gravity, Newton, Force, weight
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F=m*a
F=65 kg *9.8 m/s^2
F=637 N (Newtons) — this is the weight