If a line of sight radio communication, a distance of about 50 km is kept between the transmitting and receiving antennas. If the height of the receiving antenna is 70 m, then the minimum height of the transmitting antenna should be (Radius of the earth = 6.4×106 m)

In the line of sight communication, distance d between transmitting antenna and receiving antenna is given by d=2RhT+2RhR Here in figure,  hR and  hT  is the height of receiving and transmitting antenna, respectively.  ∴d=2RhT+2RhR ⇒50×103 = 2RhT+hR ⇒50×103 =2(6.4×106)hT+70 ⇒hT=50×1033577.7−8.37 =13.98-8.37=5.61 ⇒hT = 31.5 ≃ 32 m