Physics kinematics help plzzzzz

Question

a car travels half the distance with a speed of 20 km/hr and the other half with a speed of 30km/hr. calculate the average speed

Answer 1

20 + 30 /2 = 25 km/h

Answer 2

Yes, to ME!!!

Vavg = D/t

D/2 = 20*t1  ans D/2 = 30*t2 where t1+t2=t

t1=D/40 while t2 = D/60 so...

Vavg = D/[(D/40) = (D/60)] = 1/[(1/40) + (1/60)] = 24 km/hr

Don't ever try to average two velocities in a problem like this, you will miss it almost every time.

-Fred

Answer 3

(20+30)/2=25

Answer 4

v=d(total) /t(total) .   It is NOT simply adding the values and dividing. without a distance or time i can not cleanly solve it.

Lets just say d(total)=80km for this solution. Any amt. will work. All values will change relatively.

v=d/t

30=40km/t

t=4/3h

20=40km/t

t=2h

v(avg)=80km / (3+1/3hr)

v(avg)=24km/h