A car is on cruise control at v=30m/s. If the wind resistance is equal to. F=0.42v² what energy will the car expend to drive 1km? A)450J
B)378J
C)12.6J
D)378kJ

D)378kJ

Explanation:

Applying,

E = F×d Equation 1

Where E = Energy expanded by the car, F = Wind resistance, d = distance

From the question,

F = 0.42v² Equation 2

Susbtitute equation 2 into equation 1

E = 0.42v²d Equation 3

Given: v = 30 m/s, d = 1 km = 1000 m

Substitute these values into equation 3

E = 0.42(30²)(1000)

E = 378000

E = 378 kJ

Hence the right option is D)378kJ

work: w = fd (given)

work done by chet   =50*1 = 50 j

work done by mika =40*2 = 80 j

work done by sara =30*1.5 = 45 j

work done by bill =60*0.5 = 30 j

students in order from the greatest amount of work done to the least is mika> chet> sara> bill

hence option (b) is correct.