A young athlete has a mass of $42 \mathrm{kg}$ . On a day when there is no wind, she runs a $100 \mathrm{m}$ race in $14.2 \mathrm{seconds}$. A sketch graph showing her speed during the race is given below. The accelerating force on the athlete during the first $3.0 \mathrm{seconds}$ of the race is:

 

An astronaut has a mass of $90kg$.

Calculate her weight on the surface of the Earth.

Look at the speed-time graph of figure. Find a point where the graph is sloping upwards.

Is the parachutist accelerating or decelerating$?$

Look at the speed-time graph of figure. Find a point where the graph is sloping upwards.

Which of the two forces acting on the parachutist is greater$?$

Look at the speed-time graph of figure. Find a point where the graph is sloping upwards.

Explain the shape of the graph after the parachute has opened.

What force is needed to give a car of mass $600 kg$ an acceleration of $2.5 \raisebox{1ex}{$m$}\!\left/ \!\raisebox{-1ex}{$s^2?$}\right.$