Hooke's law. The distance d when a spring is stretched by a hanging objective varies directly as the weight w of the object. If the distance is 38 cm when the weight is 3 kg, what is the distance when the weight is 7 kg? ... ?

Hooke's law is F=-kx, which means the elastic force contained by the spring is a product of the distance it stretches and its spring constant, but the direction of the force is opposite that of the displacement. We calculate as follows:

(3 kg) (9.8 m/s^2) = - k (-0.38 m)

k = 77.4

Then use k to find the new displacement, again using Hooke's law:

(7 kg) (9.8 m/s^2) = - (77.4) x

x = - 0.89 m