4 A toy railway locomotive of mass 0.8 kg is towing a truck of mass 0.4 kg on a straight horizontal track at a constant speed of \(2 \mathrm {~m} \mathrm {~s} ^ { - 1 }\). There is a constant resistance force of magnitude 0.2 N on the locomotive, but no resistance force on the truck. There is a light rigid horizontal coupling connecting the locomotive and the truck.

1. State the tension in the coupling.
2. Find the power produced by the locomotive's engine.
   The power produced by the locomotive's engine is now changed to 1.2 W .
3. Find the magnitude of the tension in the coupling at the instant that the locomotive begins to accelerate.
   \includegraphics[max width=\textwidth, alt={}, center]{b2cd1b68-523f-40c3-8a51-acb2b55ae8c0-06_726_803_264_671} The diagram shows a block \(D\) of mass 100 kg supported by two sloping struts \(A D\) and \(B D\), each attached at an angle of \(45 ^ { \circ }\) to fixed points \(A\) and \(B\) respectively on a horizontal floor. The block is also held in place by a vertical rope \(C D\) attached to a fixed point \(C\) on a horizontal ceiling. The tension in the rope \(C D\) is 500 N and the block rests in equilibrium.