7 A sledge of mass 25 kg is on a plane inclined at \(30 ^ { \circ }\) to the horizontal. The coefficient of friction between the sledge and the plane is 0.2 .
- \begin{figure}[h]
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\caption{Fig. 1}
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The sledge is pulled up the plane, with constant acceleration, by means of a light cable which is parallel to a line of greatest slope (see Fig. 1). The sledge starts from rest and acquires a speed of \(0.8 \mathrm {~m} \mathrm {~s} ^ { - 1 }\) after being pulled for 10 s . Ignoring air resistance, find the tension in the cable. - \begin{figure}[h]
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\caption{Fig. 2}
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On a subsequent occasion the cable is not in use and two people of total mass 150 kg are seated in the sledge. The sledge is held at rest by a horizontal force of magnitude \(P\) newtons, as shown in Fig. 2. Find the least value of \(P\) which will prevent the sledge from sliding down the plane.