A van of mass $3000$ kg is pulling a trailer of mass $500$ kg along a straight horizontal road at a constant speed of $25$ms−1. The system of the van and the trailer is modeled as two particles connected by a light inextensible cable. There is a constant resistance to motion of $300$ N on the van and $100$ N on the trailer.
(i) Find the power of the van’s engine.
(ii) Write down the tension in the cable.
In first part we use total resistance to get the power. Why don't we use $300$ N? How do we imagine tension in different area (string, van and trailer)?