Explanation:
Speed has only magnitude.
Velocity has magnitude and direction.
"A bike goes 25 m/s toward main street."
This includes a direction, so it is velocity (V).
"A person walks 4 mph."
This has only magnitude, so it is speed (S).
"A plane flies 200 m/s."
This has only magnitude, so it is speed (S).
"A bird flies 100 mph due south."
This includes a direction, so it is velocity (V).
First determine the net force. Let's say the downwards force is negative and the upwards force is positive.
Since the forces act in opposite directions, the net force would be:
400N - 600N = -200N
Since I said negative is downwards, this translates to the net force being 200N downwards.
Force = mass*acceleration
200N = 60kg * acceleration
acceleration = 3.33 m/s^2