In 1993, Ileana Salvador of Italy walked 3.0 km in under 12.0 min. Suppose that during 115 m of her walk Slavador is observed to steadily increase her speed from 4.20 m/s to 5.00 m/s. How long does this increase in speed take?
vi =+245km/h aavg = -3.0m/s2
vf =vi -(0.200)vi vi =(245km/h)(1h/3600s)(103m/1km)= +68.1m/s vf =(1.000-0.200)vi =(0.800)(68.1m/s)=+54.5m/s
Δt=vf -vi /aavg
= 54.5m/s - 68.1m/s / -3.0m/s2 =-13.6m/s /-3.0 m/s2 = 4.5s