Three masses 5kg, 4kg and 7kg are aligned in a straight line as shown below. Find the net gravitational force on 4kg?
33.5 ×10−11 N
46.69 ×10−11 N
13.19 ×10−11 N
The correct option is D 13.19 ×10−11 N As gravitational force is an attractive force, the 5kg and 7kg masses attract the 4kg mass in opposite directions. So, the net force is the subtraction of the two forces acting on the 4kg mass.
The gravitation force due to 5kg on 4kg is: F1=GmMd2=6.67×10−11×4×522 =33.5×10−11N (The direction of force is towards 5 kg mass).
The gravitational force due to 7kg on 4kg: F2=GmMd2=6.67×10−11×4×722 = 46.69 ×10−11 N (The direction of force is towards 7 kg mass). Since, the force on 4 kg masses due to 5kg mass is opposite to the force due to 7kg on 4kg mass. The net force is the subtraction of both the forces. Net force on 2kg mass = (46.69−33.5)×10−11N = 13.19×10−11N.