How much power should a braked 1.5t car have to be braked to reduce its speed from 30m / s to 10m / s in 5s?

-120000 W

Explanation:

Power = change in energy / time

P = ΔE / t

P = (½ mv₂² - ½ mv₁²) / t

P = m (v₂² - v₁²) / (2t)

Given m = 1.5 t = 1500 kg, v₂ = 10 m/s, v₁ = 30 m/s, and t = 5 s:

P = (1500 kg) ((10 m/s) ² - (30 m/s) ²) / (2 * 5 s)

P = - 120000 W