A 4.0-kilogram penguin sliding across a large, flat icy surface with a constant velocity of 2.0 m s–1. Assuming that the surface is frictionless, what size force is required to keep the penguin travelling at this speed?

F=0

Explanation:

Newton's second law states that the sum of the external forces is equal to the product of the mass and the acceleration of the body

         F = m a

in this case it tells us that the velocity is constant so the acceleration must be zero,

therefore the sum of the external forces is zero; as they indicate that the surface is frictionless, there is no force applied to the system to maintain a constant speed

            F = 0

(75°f − 32) × 5/9 = 23.889°c