Odpowiedzi

2009-11-20T20:01:07+01:00
2/3 * 72 + 1/3 * 36 = 48 + 12 = 60 km/ h
2009-11-20T20:10:14+01:00
T1 = 20 min = 1/3 h
v1 =72 km/h
S2 = 10 km
v2 =36 km/h
-----------------
vśr = ?

S1 =v1*t1 = 72 km/h * 1/3 h =24 km
t2 =s2 : v2 = 10 km /36 km/h = 5/18 h
vśr = S : t ,
gdzie S = S1 +S2 =24 km + 10 km = 34 km
oraz t = t1 + t2 = 1/3 h + 5/18 h = [6/18 +5/18]h =11/18 h
vśr = S : t = 34 km/[11/18]h = 34 *[18/11] km/h =55,64 km/h
Odp. Średnia prędkość jest równa 55,64 km/h.
2009-11-20T20:22:14+01:00
Dane:
t1 = 20min =1200s
v1=72km/h = 20m/s
s2=10km = 10000m
v2=36km/h = 10 m/s

szukane:
s1=?
t2=?
v.śr=?

rozwiązanie:
s1=v1*t1
s1= 20m/s * 1200s = 24000m
s=v*t I /v
s/v=t
t2=s2/v2
t2=10000m / 10m/s = 1000s

v.śr = s1 + s2 / t1 +t2
v.śr = 24000m + 10000m / 1200s + 1000s = 34000m/2200s= 15.454545 m/s = ok 55,64 km/h