A ball is projected horizontally with a velocity of $$5 \mathrm{~ms}^{-1}$$ from the top of a building $$19.6 \mathrm{~m}$$ high. How long will the ball take to hit the ground?

The nucleus of a helium atom travels along the inside of a straight hollow tube $$4 \mathrm{~m}$$ long which forms part of a particle accelerator. If one assumes uniform acceleration, how long is the particle in the tube if it enters at a speed of $$2000 \mathrm{~m} / \mathrm{s}$$ and leaves at $$8000 \mathrm{~m} / \mathrm{s}$$

A drone is flying due west, a little above the train, with a speed of $$10 \mathrm{~m} / \mathrm{s}$$. A 270 meter long train is moving due east at a speed of $$20 \mathrm{~m} / \mathrm{s}$$. The time taken by the drone to cross the train is

The displacement $$x$$ of a particle in a straight line motion is given by $$x=1-t-t^2$$. The correct representation of the motion is