posted by Alica on .
A 1280-kg car starts from rest and accelerates to 80 km/h in 23.0 s. Friction exerts an average force of 449 N on the car during this time.
(a) What is the net work done on the car?
(b) How far does the car move during its acceleration?
(c) What is the net force exerted on the car during this time?
(d) What is the forward force exerted on the car as a result of the engine, power train, and wheels pushing backward on the road?
m =1280 kg, v =80 km/h = 22.2 m/s, t = 23 s.
W(net) = ΔKE =KE(final) – KE(initial) =
= m•v²/2 -0=1280•(22.2)²/2 =3.154•10^5 J.
v = a•t , a =v/t = 22.2/23 = 0.97 m/s²,
s= a•t²/2 = 0.97•23²/2 = 257 m.
W(net) = F(net) •s,
F(net) = W(net)/s =3.154•10^5/257 = 1227 N.
F(net) = F(applied) – F(fr) ,
F(applied) = F(net) + F(fr) = 1227+449 = 1676 N.
these are all wrong :(