Simply, apply the formula

and insert the values of m = mass, v = velocity and E = Energy.
The result will be

, m = 1 kg
Well depending on the speed of both of those things is were the rock will be placed and it also determines how fast can an environment change
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Gravitational force is given by, 
Where, m and M are the masses of the objects, R is the distance between them and G gravitational constant.
Gravitational force of the star on planet 1, 
Gravitational force of the star on planet 2, 
Ratio, 

Therefore, the gravitational force of the star on the planet 1 is three times that on planet 2.
We don't even need to know how many pulses were produced
in those 3 seconds.
The beginning of the first pulse took 3 seconds to travel
45 centimeters from the generator.
Its speed is (45 cm) / (3 sec) = 15 cm/sec.
To Make I the subject you need to get it by itself. To do this divide both sides by V and t:
I = E/Vt