Equations given are: •force(n) = mass(kg) x acceleration (m/s^2)• acceleration= change in velocitytime taken• change in velocity= acceleration x time

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 .

answer: b.

explanation: