An athlete whose mass is 89.0 kg is performing weight-lifting exercises. Starting from the rest position, he lifts, with constant acceleration, a barbell that weighs 590 N . He lifts the barbell a distance of 0.50 m in a time of 2.2 s . Use Newton's laws to find the total force that his feet exert on the ground as he lifts the barbell.

Explanation:

For this case we can begin finding the weigth associated to the athlete like this:

Now we can find the acceleration associated to the barbell using the following formula from kinematics:

We assume that the and the initial velocity is 0 so then we have:

And we can find the acceleration since we have the height and the time like this:

The mass of the barble would be:

With this acceleration we can find the apparent weigth of the barbell like this:

And finally the force exerted on the ground would be the sum of the two weigths:

at positions a, g kinetic energy is maximum.

at position d, potential energy is maximum.