4. A heavy box (mass) is dragged along the floor by a kid at a 30° angle to the horizontal with a force of 80 N (which is the maximum force the kid can apply).
a) Draw the free body diagram.
b) What is the normal force ?
c) Does the normal force decrease or increase as the angle of pull increases? Explain.
d) Assuming it begins at rest, what is its speed after ten seconds?​