When bicycle and motorcycle riders "pop a wheelie," a large acceleration causes the bike's front wheel to leave the ground. Let M be the total mass of the bike-plus-rider system; let x and y be the horizontal and vertical distance of this system's cm from the rear wheel's point of contact with the ground. What is the effect of a large acceleration on the bike's front wheel?
1) The front wheel remains on the ground
2) The front wheel lifts off the ground
3) The bike becomes unstable
4) The bike slows down