A child stands on the edge of the cliff 10 m above the ground and throws a stone horizontally with an initial speed of 5 ms−1 . Neglecting the air resistance, the speed with which the stone hits the ground will be \_\_\_\_\_\_ ms−1 (given, g=10 ms−2 ).
(1) 20
(2) 15
(3) 30
(4) 25