Final answer:
The normal force acting on a 630 N barbell when a 289 N upward force is applied and it does not lift off the ground is 341 N. This is found by using the equilibrium equation for forces perpendicular to the ground.
Step-by-step explanation:
When calculating the normal force acting on an object at rest or moving along a horizontal surface, we must look at the forces acting perpendicular to the surface. With the barbell weighing 630 N and a vertical upward force of 289 N applied, the normal force can be calculated using the equation N + F = W, where N is the normal force, F is the applied force, and W is the weight of the object.
According to Newton's third law, the total upward forces must match the downward force due to gravity when the object is in equilibrium (not moving vertically). Therefore, the normal force will adjust based on the applied force. If we substitute the given values, we get N + 289 N = 630 N. Solving for N gives us N = 630 N - 289 N = 341 N. Hence, when someone is applying a force of 289 N to the barbell, the normal force acting on it is 341 N.