Answer:
F = 50 N
Step-by-step explanation:
First we find Acceleration.
Initial Velocity(u) = 20 m/s
Final Velocity(v) = 0 m/s
Time(t) = 0.2 s
Acceleration(a) = (v - u) / t
a = (20 - 0) / 0.2
=> a = 20/0.2
=> a = 100 m/s^2
Now we know F = ma,
Mass(m) = 0.5 kg
=> F = (0.5)(100)
=> F = 50 N