$\text{Dane:}$

${\text{v}}_{\text{A}}=10\frac{\text{m}}{\text{s}}$

${\text{t}}_{\text{A}}=2\text{s}$

${\text{v}}_{\text{B}}=2,5\frac{\text{m}}{\text{s}}$

${\text{t}}_{\text{B}}=2,5\text{s}$

$\text{F}=20\text{N}$   

$\text{Szukane:}$

${\text{m}}_{\text{A}}=\text{?}$

${\text{m}}_{\text{B}}=\text{?}$

Obliczamy przyspieszenie ciała A i B:

${\text{a}}_{\text{A}}=\frac{{\text{v}}_{\text{A}}}{{\text{t}}_{\text{A}}}=\frac{10\frac{\text{m}}{\text{s}}}{2\text{s}}=5\frac{\text{m}}{{\text{s}}^2}$

${\text{a}}_{\text{B}}=\frac{{\text{v}}_{\text{B}}}{{\text{t}}_{\text{B}}}=\frac{2,5\frac{\text{m}}{\text{s}}}{2,5\text{s}}=1\frac{\text{m}}{{\text{s}}^2}$

Teraz korzystając z II zasady dynamiki Newtona obliczamy masę:

${\text{m}}_{\text{A}}=\frac{\text{F}}{{\text{a}}_{\text{A}}}=\frac{20\text{N}}{5\frac{\text{m}}{{\text{s}}^2}}=4\text{kg}$

${\text{m}}_{\text{B}}=\frac{\text{F}}{{\text{a}}_{\text{B}}}=\frac{20\text{N}}{1\frac{\text{m}}{{\text{s}}^2}}=20\text{kg}$

Poprawna odpowiedź to a)