A bullet is shot vertically downwards with an initial velocity of $100 \mathrm{~m} / \mathrm{s}$ from a certain height. Within 10 s, the bullet reaches the ground and instantaneously comes to rest due to the perfectly inelastic collision. The velocity-time curve for total time $\mathrm{t}=20 \mathrm{~s}$ will be:

(Take g = 10 m/s²).