Which of the following equations represents the law of universal gravitation
a. fg=g m1 m1 /r2
b. fg=g n/r2
c. fg=mg
d. fg=g m1 m2/r

Newton's law of universal gravitation is an INVERSE SQUARE LAW, which rules out C and D.It is proportional to the masses involved, which rules out B.A could be seen as one form of the lawF=G m1 m1/r^2Though I recognise it more as F=G m1 m2/r^2.G is the universal gravity constant and is distinct from g which is the acceleration of gravity LOCAL to a planet or moon. So, g is LOCAL, G is universal.Newton was a smart bloke, as are all these scientists whose names frequently appear. 

Isuck at math i am no sorry

    m₁v₁ + m₂v₂ = (m₁ + m₂)vmomentum is conserved.the left-hand side of the equation represents the momentum in the system before the collision.the right-hand side represents the momentum in the system after the collisionm₁ and v₁ represents the mass and the velocity of the physics blockm₂ and v₂ represents the mass and velocity of the ball of puttyv represents the final velocity of the combined mass.the question states the two masses stick together. they combined mass has its own velocity with the body mass the sum of the two objects' massestheir combined momentum is (m₁ + m₂)vto find the magitude of (m₁ + m₂)v, we need to add the vectors on the left-hand side of the equation: m₁v₁ + m₂v₂.note the diagram. i have positioned the vectors in accordance with their directions.the magnitude of the resultant can be calculated using the pythagorean theorem since this is a right triangle situation (north and west are perpendicular)|(m₁ + m₂)v| =  √[ (m₁v₁)² + (m₂v₂)² ]|(m₁ + m₂)v| =  √[ (1.5kg·8.0m/s)² + (0.40kg·20m/s)² ]|(m₁ + m₂)v| =  14.4 kg m/sfor two significant figures (assuming that 20m/s is two), this rounds to 14 kg m/s