A51.1-kg crate rests on a level floor at a shipping dock. the coefficients of static and kinetic friction are 0.622 and 0.368, respectively. what horizontal pushing force is required to (a) just start the crate moving and (b) slide the crate across the dock at a constant speed?

(a)  The force must be greater than 311.4851 N to just start the crate moving

(b)  The 184.287 N force needed to to slide the crate at constant speed      

Explanation:

We have given that mass of the crate m = 51.1 kg

Coefficient of static friction and coefficient of kinetic friction

Acceleration due to gravity

(A) Static frictional force is given by

So the force must be greater than 311.4851 N to just start the crate moving

(b) For sliding the crate across the dock at a constant speed force must be equal to kinetic friction force

Kinetic friction force is given by

So the 184.287 N force needed to to slide the crate at constant speed

air exerts forces on falling objects near earth’s surface.

explanation:

the term 'free falls' refer to object that are falling towards the earth, in a situation in which gravity is the only force acting on the object.

for an object in free fall, the acceleration is constant (g, the gravitational acceleration), and so the velocity of the object constantly increases.

for objects near earth's surface, there is always another force acting on the object: the resistance due to the air. this force is opposed to the direction of fall of the object, and it is proportional to the velocity of the object, so as the object falls down, this force increases up to a point when it balances the force of gravity, and the object continues its motion at constant velocity (called terminal velocity). since in this case gravity is not the only force acting on the object, we are not in a situation of free fall.

continuous conducting path for current, power supply