Mass = 0.4kg
force = 8N
acceleration = 8/0.4 = 20 m/s²
Assume direction from south to north as positive,
at the instant when the force acts,
u = 10 m/s
a = -20 m/s²
x₀ = 0
x = x₀ + ut + 0.5at²
a)before t=0s, force was not acting
so 0 = x + ut
⇒ 0 = x + 10×(5)
⇒ x = -50m
So particle was 50m south of x=0 at t=-5s.
b)at t = 25s,
x = 10×25 - 0.5×20×25² = -6000 m
So particle is at 6000m south of x=0 at t=25s.
c)at t = 30s,
x = 10×30 - 0.5×20×30² = -8700 m
So particle is at 8700m south of x=0 at t=30s.