Answer:
Given, Apparent weight(W₂)=4.2N
Weight of liquid displaced (u)=2.5N
Let weight of body in air = W₁
Solution,
U=W₁-W₂
W₁=4.2=2.5=6.7N
∴Weight of body in air is 6.7N
The distance between the two charges is 
Explanation:
The electrostatic force between two charged objects is given by Coulomb's law:

where:
is the Coulomb's constant
are the charges of the two objects
r is the separation between the two charges
In this problem, we are given the following:



Therefore, we can rearrange the equation to solve for r, the distance between the two charges:

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Answer:
1.38 x 10^-18 J
Explanation:
q = - 1.6 x 10^-19 C
d = 5 x 10^-10 m
the potential energy of the system gives the value of work done
The formula for the potential energy is given by

So, the total potential energy of teh system is

As all the charges are same and the distance between the two charges is same so the total potential energy becomes

K = 9 x 10^9 Nm^2/C^2
By substituting the values

U = 1.38 x 10^-18 J
Yes, if we know the Earth's mass
Explanation:
The momentum of an object is a vector quantity given by the equation

where
m is the mass of the object
v is its velocity
In this case, we are asked if we can find the velocity of the Earth by starting from its momentum. Indeed, we can. In fact, we can rewrite the equation above as

Therefore, if we know the momentum of the Earth (p) and we know its mass as well (m), we can solve the formula to find the Earth's velocity.
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