Two boxes, P and Q, are at rest on a frictionless horizontal surface. A light, flexible cord connects them. The mass of P is greater than the mass of Q.

(As shown in the diagram,) A horizontal force of magnitude F is applied to box Q, causing both boxes to accelerate to the right.

What best describes the magnitude of the force exerted by the connecting cord on box P?

*equal to F

*greater than F

*zero

*less than F, but greater than zero

the answer is less than F, but greater than zero

The boxes are tied together, so their motions are equal ... displacement, velocity, and acceleration ... the same for both boxes once they get going.

The force (F) exerted on Q has to be enough to accelerate the mass of both boxes.

But the force of the string pulling box-P is only enough to move the mass of box-P with the same acceleration.

So the magnitude of the force exerted on box-P by the string (the tension in the string) is less than F, (but greater than zero, because it accelerates box-P).

It doesn't matter which box is heavier, lighter, more mass, or less mass.