Question

Three masses 5kg, 2 Kg, and 7 Kg are aligned in a straight line as shown below, find the net gravitational force on 4 Kg?

• A. Zero
• B. 33.5×10^-11 N
• C. 46.69×10^-11 N
• D. 13.19×10^-11 N

Answer 1

The correct option is D

13.19×10^-11 N

5 Kg and 7 Kg masses attract the 4Kg mass in opposite direction.So, the the net force is subtraction. The gravitational force due to 5 Kg on 4 Kg is:

F = $\frac{GmM}{d^2}$

F = 5$\times$G = $33.5\times {10}^{-11}$ N ( The direction of force is towards 5 Kg mass)

The gravitational force due to 7 kg on 4 Kg :

F = $\frac{GmM}{d^2}$

F = 7$\times$G = $46.69\times {10}^{-11}$ N (the direction of force is towards 7 Kg mass)

Since the force on 2 Kg mass due to 5 kg mass is opposite to the force due to 7 kg on 2 kg mass. The net force is the subtraction of both forces.

Net force on 2 Kg mass = (46.69 - 33.5)$\times$ ${10}^{-11}$​N = 13.19$\times$${10}^{-11}$​​ N