A cart moves horizontally along a straight line with constant speed 30ms−1. A particle is fired vertically upwards from the moving cart so that it returns to the cart at the same point from where it was projected after the cart has moved 80m. At what speed, relative to the cart, must the projectile be fired? Take g=10ms−2.
(1) 10ms−1
(2) 108ms−1
(3) 340ms−1
(4) None of these