1. dane: v = 20 m/s s = 40 m g = 10 m/s2 szukane: f = ? F = T ma = fmg /:m a = gf /:g f = a/g s = vt -1/2 at^2 v = at /:a t = v/a s = vt -1/2 at^2 s = v*v/a -1/2 a(v/a)^2 = v^2/a -1/2 av^2/a^2 = v^2/a -v^2/2a = = 2v^2/2a -v^2/2a = v^2/2a s = v^2/2a I*2a 2sa = v^2 .:2s a = v^2/2s f = a/g = v^2/2s:g = v^2/2gf f = (20m/s)^2/(2 *10m/s2 *40m) f = 0,5 ====== 2. dane: m1 = 5 kg m2 = 10 kg F = 50 N f = 0,2 g = 10 m/s2 = 10 N/kg szukane: a) a = ? b) Fn = ? a) Przyspieszenie układu klocków. Z II zasady dynamiki: T1 = fm1g T2 = fm2g am1 = N-T1 am2 = F-T2-N ---------------- dodajac stronami otrzymujemy: a(m1+m2) = F-T1-T2 /:(m1+m2) a = (F-T1-T2)/(m1+m2) = (F-gfm1-gfm2)/(m1+m2) = [F -fg(m1+m2)]/(m1+m2) = = F/(m1+m2) -gf a = F/(m1+m2) - gf = 50N/(5kg+10kg) - 10N/kg* 0,2 a = 1,33 N/kg a = 1,33 m/s2 ============= b) Siła naciągu: Fn = fm1/(m1+m2) = 50N *5kg/(5kg+10kg) Fn = 3,33 N ===========
