Newton's law of gravitation says that the magnitude f of the force exerted by a body of mass m on a body of mass m is f = gmm r2 where g is the gravitational constant and r is the distance between the bodies. (a) find df/dr. df dr = − 2gmm r3 what is the meaning of df/dr? df/dr represents the rate of change of the mass with respect to the distance between the bodies. df/dr represents the amount of force per distance. df/dr represents the rate of change of the mass with respect to the force. df/dr represents the rate of change of the distance between the bodies with respect to the force. df/dr represents the rate of change of the force with respect to the distance between the bodies. what does the minus sign indicate? the minus sign indicates that as the distance between the bodies increases, the magnitude of the force decreases. the minus sign indicates that the bodies are being forced in the negative direction. the minus sign indicates that the force between the bodies is decreasing. the minus sign indicates that as the distance between the bodies increases, the magnitude of the force increases. the minus sign indicates that as the distance between the bodies decreases, the magnitude of the force remains constant. (b) suppose it is known that the earth attracts an object with a force that decreases at the rate of 4 n/km when r = 20,000 km. how fast does this force change when r = 10,000 km? n/km