A constant force is exerted on a cart that is initially at rest on an air 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
A.
four times as long as that for the stronger force.
B.
twice as long as that for the stronger force.
C.
equal to that for the stronger force.
D.
half as long as that for the stronger force.
E.
a quarter of that for the stronger force.