Step 1: Collect the data and convert to SI units.
Mass $m = 50\ g = 0.05\ kg$, initial speed $u = 50\ \text{cm s}^{-1} = 0.5\ \text{m s}^{-1}$, final speed $v = 0$ (it stops), and time $t = 0.5\ s$. We want the stopping force.
Step 2: Decide on the approach.
Force relates to the rate of change of momentum, so the impulse-momentum idea is the cleanest path here.
Step 3: Find the change in momentum.
\[ \Delta p = m(v - u) = 0.05(0 - 0.5) = -0.025\ \text{kg m s}^{-1} \]
Step 4: Relate force to momentum change.
By Newton's second law in impulse form, \[ F = \frac{\Delta p}{t} = \frac{-0.025}{0.5} \]
Step 5: Compute the value.
\[ F = -0.05\ N \]
Step 6: Interpret the result.
The negative sign just shows the force opposes the motion; its magnitude is $0.05\ N$, matching option (2). \[ \boxed{0.05\ N} \]