A car of mass $1200 \mathrm{kg}$ accelerates from rest to a speed of $8.0{ \mathrm{m} \mathrm{s}}^{-1}$ in a time of $2.0 \mathrm{s}$. At high speeds the resistive frictional force $\mathrm{F}$ produced by air on a body moving with velocity $\mathrm{v}$ is given by the equation $\mathrm{F}={\mathrm{bv}}^2$, where $\mathrm{b}$ is a constant. Use your value of $\mathrm{b}$ and the driving force to calculate the acceleration of the car when the speed is $30{ \mathrm{m} \mathrm{s}}^{-1}$.

A car of mass $1200 \mathrm{kg}$ accelerates from rest to a speed of $8.0{ \mathrm{ms}}^{-1}$ in a time of $2.0 \mathrm{s}$. At high speeds the resistive frictional force $\mathrm{F}$ produced by air on a body moving with velocity $\mathrm{v}$ is given by the equation $\mathrm{F}={\mathrm{bv}}^2$, where $\mathrm{b}$ is a constant. Sketch a graph showing how the value of $\mathrm{F}$ varies with $\mathrm{v}$ over the range $0$ to $50 \mathrm{m}{\mathrm{s}}^{-1}$. Use your graph to describe what happens to the acceleration of the car during this time.

Explain what is meant by the mass of a body and the weight of a body.

 State and explain one situation in which the weight of a body changes while its mass remains constant.

State the difference between the base units of mass and weight in the SI system.

State Newton's second law of motion in terms of acceleration.

 When you jump from a wall on to the ground, it is advisable to bend your knees on landing. State how bending your knees affects the time it takes to stop when hitting the ground.

When you jump from a wall on to the ground, it is advisable to bend your knees on landing. Using Newton's second law of motion, explain why it is sensible to bend your knees.