A 30.0 kg dolphin decelerates from 12.0 to 7.00 m/s in 2.60 s to join another dolphin in play. What average force (in N) was exerted to slow him if he was moving horizontally? (The gravitational force is balanced by the buoyant force of the water. Assume the positive direction is in the direction of motion. Indicate the direction with the sign of your answer.)

Force is 57.69 N to the opposite direction of motion of dolphin.

Explanation:

We have force is the product of mass and acceleration.

That is

Force = Mass x Acceleration

F = ma

Mass of dolphin, m = 30 kg

We have equation of motion, v = u + at

Final velocity, v = 7 m/s

Initial velocity, u = 12 m/s

Time, t = 2.60 s

Substituting

7 = 12 + a x 2.6

a = - 1.92 m/s²

Force, F = 30 x - 1.92 = - 57.69 N

So the force is 57.69 N to the opposite direction of motion of dolphin.