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 $1.2 \mathrm{kg}{ \mathrm{m}}^{-3}$.

Figure shows the force- extension graph for a wire that is stretched and then released.

Force-extension graph for a wire.

(a) Which point shows the limit of proportionality?

Figure shows the force- extension graph for a wire that is stretched and then released.

Force-extension graph for a wire.

(b) Which point shows the elastic limit ?

Figure shows the force- extension graphs for four springs, A, B, C and D.

Force-extension graphs for four different springs.

(a) State which spring has the greatest value of force constant.

Figure shows the force- extension graphs for four springs, A, B, C and D.

Force-extension graphs for four different springs.

(b) State which is the least stiff.

Figure shows the force- extension graphs for four springs, A, B, C and D.

Force-extension graphs for four different springs.

(c) State which of the four springs does not obey Hooke's law.

List the metals in Table from stiffest to least stiff.

The Young modulus of various materials. Many of these values depend on the precise composition of the material concerned. $\left(\text{Remenber} 1\mathrm{GPa}={10}^9\mathrm{Pa}\right)$

Which of the non-metals in Table is the stiffest?

The Young modulus of various materials. Many of these values depend on the precise composition of the material concerned.$\left(\text{Remenber} 1\mathrm{GPa}={10}^9\mathrm{Pa}\right)$

Figure shows stress- strain graphs for two materials, A and B. Use the graphs to determine the Young modulus of each material.

Stress-strain graphs for two different materials.