The length of a spring varies directly with the mass of an object that is attached to it. When a 30 -gram object is attached, the spring stretches 9 centimeters. Which equation relates the mass of the object, m , and the length of the spring, s ?

Because the spring length varies directly with the mass, write s = km for some constant k. Using the given values, k = 9/30 = 3/10, so the relationship is s = (3/10)m. This matches choice A, “s is equal to 3 tenths m.”

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