constant force is exerted on a cart that is initially at rest on a track. Friction between the cart and the track is negligible. The force acts for a short time interval and gives the cart a certain final speed. To reach the same final speed with a force that is only half as big, the force must be exerted on the cart for a time interval that for the stronger force. a. B C. d. Four times as long as Twice as long as Equal to Half as long as A quarter of