rowerzysta pierwsze 40 km przejechał z predkoscią 36km/h , a nastepnie 40 km z predkoscia 24 km/h. Oblicz predkosc srednia.

S1 = 40 km S2 = 40 km S = 80 km v1 = 36 km/h v2 = 24 km/h zatem t1 = S1/v1 = 40 km/36 km/h = 10/9  h t2 = S2 /v2 = 40 km/ 24 km/h =  5/3  h czyli v sr = S / [ t1 + t2 ] = 80 km / [ 10/9 + 5/3] h = 80 km / [ 10/9 + 15/9 ] h = = 80 km / ( 25/9) h = [ 80 *(9/25)] km/h = 28,8 km/h =====================================================

t1 = s/v1 t2 = s/v2   => s/v1 + s/v2 = s (1/v1 + 1/v2) = s (v1 + v2 / v1* v2) Vśr =  2s * v1 * v2 / s*(v1+v2) = 2 v1 * v2 / (v1+v2) Vśr = 28.8 km/h