From the top of a 60 m high tower, a stone is projected vertically upward with speed 20 m s⁻¹. Taking g=10 m s⁻², its average speed until it reaches the ground is:
Options

Question

From the top of a 60 m high tower, a stone is projected vertically upward with speed 20 m s⁻¹. Taking g=10 m s⁻², its average speed until it reaches the ground is:

G1 Physics · Accepted Answer

Time to hit the ground is found from −60 = 20t − 5t² ⇒ t²−4t−12=0 ⇒ t=6 s. The stone rises an additional height H₁ = 20²/(2×10)=20 m. Total distance travelled: 20 m upward + (20+60) m downward = 100 m. Average speed = 100/6 = 50/3 m s⁻¹.