Answer:
Friction between the box and the floor is 25N to the left.
Explanation:
According to Newton's second law of motion, the net force acting on an object is equal to the produce between the object's mass and its acceleration:

where
m is the mass of the object
a is its acceleration
In this problem, we have two forces acting on the object:
- The applied force, F = 25 N, to the right
- The force of friction
, opposing the motion of the box, so to the left
So we can write the net force as

Also, we know that the box is moving at constant speed: this means its acceleration is zero, so

Therefore

WHich means:

And therefore,

which means that the force of friction is also 25 N.
Answer:
Part a)

Part b)

Explanation:
Part a)
If block is sliding up then net force must be zero and friction will be in opposite to the direction of motion of the block


so we have





Part b)
If block is sliding down then net force must be zero and friction will be in opposite to the direction of motion of the block


so we have





Answer:
F=2627.6N
Explanation:
The work done by this resistive force while traveling a distance <em>d</em> underwater would be:

where the minus sign appears because the force is upwards and the displacement downwards.
This work is equal to the change of mechanical energy. At the diving plataform and underwater, when she stops moving, the woman has no kinetic energy, so all can be written in terms of her total change of gravitational potential energy:

Putting all together:
