一、填空題1. A particle is at rest at t = 0 and starts moving along the x axis from the origin. Based on the following figure, the displacement at t = 9 s is ___(1)___ (m).

5. The following metal objects, a disk, a solid sphere, a hollow sphere, and a loop have the same radius and mass. Assuming they are released from the same point on a ramp at rest and start rolling down, which one will take the shortest time to reach the bottom of this ramp? ___(6)___