David Sang and Graham Jones Solutions for Chapter: Matter and Materials, Exercise 5: Questions

(a) Why is it difficult to hold an inflated plastic ball underwater?

(b) A submarine floats at rest under the water. To rise to the surface compressed air is used to push water out of its 'ballast' tanks into the sea. Why does this cause the submarine to rise?

A boat has a uniform cross-sectional area at the water line of $750{ \mathrm{m}}^2$. Fifteen cars of average mass $1200 \mathrm{kg}$ are driven on board. Calculate the extra depth that the boat sinks in water of density $1000 \mathrm{kg}{ \mathrm{m}}^{-3}$.

A balloon of volume $3000{ \mathrm{m}}^{-3}$ is filled with hydrogen of density $0.090 \mathrm{kg}{ \mathrm{m}}^{-3}$. The mass of the fabric of the balloon is $100 \mathrm{kg}$. Calculate the greatest mass that the balloon can lift in air of density $1.2 \mathrm{kg}{ \mathrm{m}}^{-3}$.