Three identical very dense masses of 7600 kg each are placed on the x axis. One
ID: 1437781 • Letter: T
Question
Three identical very dense masses of 7600 kg each are placed on the x axis. One mass is at x_1= -120 cm, one is at the origin, and one is at x_2 =410 cm. What is the magnitude of the net gravitational force F_grav on the mass at the origin due to the other two masses? Take the gravitational constant to be G = 6.67 times 10^-111 N m^2/kg^2. Express your answer in newtons to three significant figures. What is the direction of the net gravitational force on the mass at the origin due to the other two masses?Explanation / Answer
The formula to use is F = GMm/r2. Find the force from x1 and x3, one at a time. Remember that the first force will be negative (going to the left) and the second force will be positive (going to the right). But the overall force will be positive, because Mastering Physics only wants the magnitude:
F1 = GMm/r2
F1 = (6.67*10^-11) * 7600 * 7600 / -(1.20^2)
F1 = -2.675*10^-3 N
F2 = GMm/r2
F2 = (6.67*10^-11) * 7600 * 7600 / (4.10^2)
F1 = 2.29*10^-4 N
Fgrav = F1 + F2
Fgrav = -2.675*10^-3 +2.29*10^-4
Fgrav = -2.446*10^-3
Make this overall force positive, since Mastering Physics only wants the magnitude:
Fgrav = -2.446*10^-3
The answer just depends on which force from Part A was larger (whether mass 1 or mass 2 was closer to the origin). Since the force from the mass on the left was larger, the object at the origin will move to the left. This is in the -x direction.
-x direction
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