6-a).
Force = (mass) x (acceleration)
Net force on the trolley = (20 kg) · (0.5 m/s²) =
Net force on the trolley = 10 Newtons.
6-b).
But you're pushing it with 15N of force.
Something mysterious is fighting your force, and
pushing the trolley BACKWARDS with 5N of force.
THAT's the effect of friction.
7-a).
F = (mass) x (acceleration)
Divide each side by (mass):
Acceleration = (force) / (mass)
For the car,
Acceleration = (-5,000 Newtons) / (1,000 kg)
Acceleration = -5 m/s² .
7-b).
change in velocity= acceleration x time
change = (-20 m/s)
-20 m/s = (-5 m/s²) · (time)
Divide each side by (-5 m/s²) :
Time = (-20 m/s) / (-5 m/s²)
Time = 4 seconds .
