In order to slide a heavy desk across the floor at constant speed in a straight line, you have to exert a horizontal force of 400 newtons. compare the 400-newton horizontal pushing force f to the frictional force f between the desk and the ground.
1. f < f; the frictional force is greater than the pushing force since it is such a heavy desk.
2. f = f from newton’s first law.
3. f > f; the frictional force is always less than any other force acting on the object.
4. it depends on the direction the desk moves. 5. f = f from newton’s third law.

F = f from Newton’s first law.

Explanation:

since the desk is moved in a straight line at a constant speed, newton first law tell us that the two forces must be equal.

Newton's First Law states that an object will remain at rest or in uniform motion in a straight line unless acted upon by an external force. since the table has been set in motion by the 400 N force, it will remain in motion unless it is been acted upon by an external force, and this means that the 400 N must be equal to the frictional force for it to have been in motion in the first instance.

an obstruction

explanation:

v=uf/(u-f)

= 5.-10/(5+10) convex lens has negative focal length