During summers why do people feel more hot in Delhi than people living in Mumbai ?

 During the summer months, the sun shines brighter on the northern latitudes. Delhi being North of Mumbai gets more Sun during these months.

Because of the strong sun, the environment, and the air around Delhi and other Northern states becomes warmer and lighter and rises up creating a low-pressure area that is filled in by the winds from the west, ie, the Thar Desert in Rajasthan. This wind from the west known as Loo moves in over Northern India and is the cause of real hot temperatures in Summer.

Mumbai, being a coastal city enjoys a maritime climate and is not affected by such phenomena as in Delhi. The temperature in coastal cities/areas is regulated because of the exchange of Land and Sea Breezes.