i have a question about work = force * distance.?

Question

so when there is a force applies on an object, and the object moves. Does it accelerates or moves at a constant speed?

Answer 1

Newton's II Law says:
sum of the forces = mass * acceleration

so if there is a net force, then there must be acceleration, so it does not move with constant speed unless the sum of the forces is zero
now, if the force is constant, it will move with constant acceleration, otherwise not

work = force * distance is valid only if the force acts parallel to the line of motion (angle between the displacement vector and the force vector is zero), otherwise
work = force*distance*cosine of the angle between the displacement and the force (which, in mathematics, is called the dot product of F and displacement)

Answer 2

If an object is on a surface assumed to be frictionless, or in a weightless environment, it would accelerate under an applied force. If an object is on a horizontal surface and there is friction, and lets say the object is in motion with a force applied in the direction of motion, then it is possible that the friction force and the applied force exactly cancel each other. In that case the object would move at a constant speed. Again, if an object is on an inclined plane you can have acceleration or constant speed depending on the angle of the inclined plane, the coefficient of friction, and the magnitude of the forces.

Answer 3

The object accelerates based on the formula
Force = mass x acceleration. This is called Newton's
Second law of motion. It will accelerate until an opposing force limits further speed. Like terminal velocity of a parachutist,limited by atmospheric resistance v. the acceleration produced by gravity

Answer 4

If you set an object in motion, it will maintain a constant speed it you maintain a force sufficient to overcome the ambient friction and any changes in elevation which of course will change the gravitational effect on the moving object.

So in summary, if you are on a level plane and have an object in motion, you can maintain a constant speed by applying sufficient force to negate any frictional opposition.

Answer 5

The other answers are pretty much correct, just tought to add that Newton's second law is a bit more general than what the previous posters have said. It actually says that the sum (vectorial sum) of all the forces acting on a system is equal to the variation of the momentum over time, that is, the first derivative of the momentum over time.
Since momentum = mass*velocity, in the case of a system with constant mass, you get sum of forces = mass * d(velocity)/dt = mass*acceleration

Answer 6

assuming a constant force, the object will accelerate (assuming the force exceeds the force holding it still) until the forces are equal. with no forces to hold it back (i.e. a vacuum) the object will accelerate indefinitely.