The electrostatic force between two charges Q1 and q is given by

where
ke is the Coulomb's constant
Q1 is the first charge
q is the second charge
r is the distance between the two charges
Re-arranging the formula, we have

and since we know the value of the force F, of the charge Q1 and the distance r between the two charges, we can calculate the value of q:

And since the force is attractive, the two charges must have opposite sign, so the charge q must have negative sign.
Answer:
0.098 N
Explanation:
From the question,
Spring scale reading = W-U............... Equation 1
Where W = weight of the cube, U = upthrust.
W = mg
Where m = mass of the cube, g = acceleration due to gravity.
Given: m = 11 g = 0.011 kg, g = 9.8 m/s².
W = 0.011(9.8)
W = 0.1078 N.
From Archimedes principle,
Upthrust = weight of water displaced.
U = (Density of water×volume of metal cube)×acceleration due to gravity.
U = (D×V)g
Given: D = 1000 kg/m², V = 1 cm³ = (1/1000000) = 1×10⁻⁶ m³, g - 9.8 m/s²
U = 1000(9.8)(10⁻⁶)
U = 0.0098 N.
Substitute the value of W and U into equation 1
Reading of the spring scale = 0.1078-0.0098
Reading of the spring scale = 0.098 N
Another name is voltaic battery
The initial kinetic energy of the boat and its rider is

After Sam stops it, the final kinetic energy of the boat+rider is

because its final velocity is zero.
For the law of conservation of energy, the work done by Sam is the variation of kinetic energy of the system:

where the negative sign is due to the fact that the force Sam is applying goes against the direction of motion of the boat.
Answer:
<h2>Mass of 1 Kg and 2 Kg, 1 meters apart.</h2>
Explanation:
The gravitational force is defined as

By definition, the gravitational force depends directly on the product of the masses and indirectly on the distance between the masses, which means the further they are, the less gravitational force would be. And, the greater the masses, the greater the gravitational force.
Among the options, the pair that would have the greatest gravitational force is Mass of 1 Kg and 2 Kg, with 1 meter between them.
Notice that the last choice includes the same masses but with a greater distance between them, that means it would be a weaker graviational force.
Therefore, the right answer is the second choice.