Teaching Physics with the Physics Suite

Edward F. Redish

Sample Problems

Nathan's train

Little Nathan’s dad has hooked together two boxes with ropes to make a train for him as shown in the picture. Nathan has put one of his twin sisters in each box and is pulling them along the rug as shown.

(a) If Nathan is pulling on the rope with a constant force T, draw free body diagrams for each of the boxes, identify all the forces on it, being sure to specify the kind of force each one is and what object is exerting it.

(b) Draw a free-body diagram for rope 2 (the one connecting the two boxes). Assume the rope is very light so that you can ignore its weight.

(c) Nathan is pulling his train so it is moving at a constant speed. If any of the forces in your three diagrams are equal, identify them and say how you know.

Page last modified September 28, 201: D40