Question

# State the universal law of gravitation.  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?    [5 MARKS]

Solution

## Definition: 2 Mark Problem: 3 Mark 1. The universal law of gravitation states that every object in the universe attracts every other object with a force called the gravitational force. The force acting between two objects is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers. 2. 5 kg and 7 kg masses attract the 4 kg mass in opposite direction. So, the net force is subtraction. The gravitation force due to 5 kg on 4 kg is: F = GmMd2 F = 5 × G = 33.5 × 10−11 N (The direction of force is towards 5 kg mass) The gravitational force due to 7 kg on 4 kg: F = GmMd2 F = 7 × G = 46.69 × 10−11​N (The direction of force is towards 7 kg mass). Since the force on 2 kg masses 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 the forces. Net force on 2 kg mass = (46.69 - 33.5) × 10−11​​ N = 13.19 × 10−11 ​​N.

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