Question

A sprinter from rest accelerates at 1.5m/s² for the first 20m but then gets tired and decelerates at -0.1m/s² for the next 80m. what is the sprinters final velocity?

Answer 1

u = 0

a₁ = 1.5 m/s²

S₁ = 20 m

a₂ = -0.1 m/s²

S₂ = 80 m

v₁² = u₁² + 2a₁S₁

v₁² = 2 x 1.5 x 20 m²/s² = 60 m²/s²

v₁ = 2√15 m/s

v₂² = v₁² + 2a₂S₂ = 60 - 2 x 0.1 x 80  m²/s² = 60 - 16  m²/s² = 44 m²/s²

v₂ = 2√11 m/s (Ans)