II zasada dynamiki Newtona:
a = \frac{F}{m}
a = \frac{2s}{t^2}
s = 3000 cm = 30 m
t = 20 s
a = \frac{2*30 m}{(20 s)^2} = \frac{60 m}{400s^2} = 0,15 m/s^2
Dane:
F = 9N = 9 \frac{kg * m}{s^2}
a = 0,15 m/s^2
m = ?
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m = \frac{F}{a}
m = 9 \frac{kg * m}{s^2} / 0,15 \frac{m}{s^2}
m = 60 kg