Final answer:
To maintain constant velocity while sliding a 120-kg crate across a level floor, you need to exert a force equal to the kinetic frictional force opposing the crate's motion. This force, Fp, is found by multiplying the coefficient of kinetic friction by the normal force, which is the crate's weight on Earth.
Step-by-step explanation:
To keep a 120-kg crate sliding along the floor with constant velocity, the force you need to exert on the crate, denoted as Fp, must be equal to the force of kinetic friction opposing the crate's motion. According to Newton's first law of motion, an object in motion will remain in motion with a constant velocity if the net force acting on it is zero. This means that the frictional force must be balanced by the applied force, Fp, to maintain a constant velocity.
The magnitude of the force of kinetic friction (f-k) can be calculated using the coefficient of kinetic friction (μk) and the normal force (N), which is equal to the weight of the crate if it's on a horizontal surface. The equation is f-k = μk × N. Since the crate has a mass of 120 kg and is on Earth, where gravitational acceleration (g) is approximately 9.8 m/s2, the normal force is N = mass × g = 120 kg × 9.8 m/s2. With the given coefficient of kinetic friction you could then find Fp.
If the coefficient of kinetic friction is not provided, it is impossible to calculate Fp without additional information. However, if you have been given a coefficient of kinetic friction, then you just substitute the values into the formula f-k to find the applied force required for constant velocity.