A cable loaded with 0.5 tonne per horizontal metre span is stretched between supports in the same horizontal line 400 m apart. If central dip is 20 m, the minimum tension in the cable, will be A. 200 tonnes at the centre B. 500 tonnes at the centre C. 200 tonnes at the right support D. 200 tonnes at the left support

The correct answer is A. 200 tonnes at the centre.

The cable is loaded with 0.5 tonne per horizontal metre span, so the total load on the cable is 0.5 * 400 = 200 tonnes. The central dip is 20 m, so the cable is in equilibrium under the forces of gravity and tension. The tension in the cable at the centre is equal to the weight of the cable, which is 200 tonnes.

Option B is incorrect because the tension in the cable is not equal to the total load on the cable. The tension in the cable is equal to the weight of the cable, which is 200 tonnes.

Option C is incorrect because the tension in the cable is not equal to the tension at the centre. The tension in the cable is equal to the weight of the cable, which is 200 tonnes.

Option D is incorrect because the tension in the cable is not equal to the tension at the left support. The tension in the cable is equal to the weight of the cable, which is 200 tonnes.