Where needed, use \(g=10\text{ m s}^{-2}\).

A particle is projected vertically upwards with speed \(40\text{ m s}^{-1}\) alongside a building of height \(h\) m.

(a) The particle is above the level of the top of the building for 4 seconds. Find \(h\). [4]

(b) One second after the first particle is projected, a second particle is projected vertically upwards from the top of the building with speed \(20\text{ m s}^{-1}\). Let \(t\) seconds denote the time after projection of the first particle. Find \(t\) when both particles are at the same height above the ground. [4]