Speed and acceleration

Question

A boy on a bicycle is going downhill at 16km/h.  If his brakes fail and he accelerated at 0.3m/s², what speed will he attain if the hill is 400m long?

Answer 1

The first thing you need to do is convert everything to the same units, usually meters (m) and seconds (s).

v_i = (16 km/h)(1000 m/1 km)(1 h/3600 s) = 4.444 m/s

a = 0.3 m/s²

Δx = 400 m

(your class may use d or another variable in place of Δx)

 

Velocities, acceleration and distance are related by the equation (v_i is initial/starting velocity, and v_f is the final/ending velocity)

v_f² = v_i² + 2aΔx

 

You have values for everything but v_f, so plug them in and solve.