We have a cart of mass 3 kg, with a cord tied to it. We pull the cord with a force of 15 Newtons at an angle of 30° above horizontal, as the diagram shows. The friction with the floor is small, maybe 0.1 Newtons, so ignore it.
a) If we pull the cart keeping the tension constant at 15 Newtons, how fast will it be going after it moves 5 meters, if it starts from rest?
b) Now add mass to the cart, another 3 kg, and pull with the same force, at the same angle, again for 5 meters. How fast will the cart be moving?
c) It would be a reasonable first reaction to think that, with twice the mass, the cart will have half the acceleration, so it will end up moving half the speed. That was the reasoning for Xena and Yara on the exam. Why doesn't that reasoning work here?