Question

two bodies of masses 2kg and 4 kg are placed at a distance of 20 cm from each other calculate gravitational force on 1 kg mass placed at the centre of line joining two bodies

Answer 1

First you need to know the gravitational force equation:

$F=\frac{KM_{1}M_{2}}  {r^{2}}$

Where:

• K=Gravitational constant($6.67X10^{-11}$)
• $M_{1}$=Mass of object 1
• $M_{2}$=Mass of object 2
• r=Distance between the two object's centers(in metres)

Since the 1 kg mass is placed between the two bodies, therefore the distance between the 1 kg mass and either of the bodies is 0.1 m

Three seperate calculations are required.

First, the gravitational force that the 2 kg mass exerts on the 1 kg mass:

$\frac{(6.67X10^{-11})X2X1} {0.1^{2}} =1.334X10^{-8}$

Secondly, the gravitational force that the 4 kg mass exerts on the 1 kg mass:

$\frac{(6.67X10x^{-11})X2X4} {0.1^{2}}$=$2.668X10^{-8}$

Thirdly, we need to calculate the net gravitational force on the 1 kg mass factoring in direction since force is a vector quantity:

$(2.668X10^{-8})-(1.334X 10^{-8} )=1.334X10^{-8} N$

Note: The question did not allow for direction but direction must always be given in an answer when dealing with force.