Question 3 Help Please

Question

A ball has a diameter of 7.0 cm, and a mass of 400 g. Will it float or sink when thrown into a lake? Please explain. (Just in case, the volume of a sphere is (4/3)PixR³)

Answer 1

You need to compare the weight of the water that WOULD HAVE BEEN THERE if the ball were not and then compare that to the weight of the ball. If the weight of the ball is more, the ball will sink. If the weight of the ball is less, then the ball will float.

To calculate the weight of the water, first calculate the volume of the ball. That volume of water was what was displaced.

V = (4/3)πr³ but use r = 3.5 cm since the radius is half the diameter.

Then multiply your result by the density of water which is 1 g/cm³ (hint: multiplying be 1 does not change the numerical result)

This gives you the mass of the water that would have been there if the ball was not.

Now compare the answer from above to the mass of the ball at 400 g. Is the ball heavier or lighter? If lighter, the ball floats.