State the meaning of work done.
A skier is towed across horizontal ground by a wire fixed to a kite, as shown in Fig. 3.1. The skier travels in a straight line over the ground at a steady speed of $4.4\,\text{m s}^{-1}$. The wire makes an angle of $30^\circ$ to the horizontal. The tension in the wire is $140\,\text{N}$. Calculate the work done by the tension to move the skier for $30\,\text{s}$.
The skier has a weight of $860\,\text{N}$. The vertical component of the tension in the wire and the skier’s weight together produce a downward pressure on the ground of $2400\,\text{Pa}$. Determine the total area of ski contact with the ground.
The wire attached to the kite is uniform. Its stress is $9.6 \times 10^6\,\text{Pa}$. Calculate the diameter of the wire.
The graph of tension $F$ against extension $x$ for the wire in (b) is shown in Fig. 3.2. A gust of wind raises the tension in the wire from $140\,\text{N}$ to $210\,\text{N}$. Calculate the change in the strain energy stored in the wire.