A rock is thrown straight up in the air from an initial height h., in metres, with initial velocity vg, in metres per second. The height in metres above the ground after t seconds is given by h(t) = -4.9r² + vt + ho. Find an expression for the time it takes the rock to reach its maximum height.

( x - 273,000 ) / x = 0.4

Matthew is attending a very loud concert. To avoid permanent ear damage, he decides to move farther away from the stage. Sound intensity is given by the formula I= k/d^2, where k is a constant and d is the distance in metres from the listener to the source of the sound. Determine an expression for the decrease in sound intensity if Matthew moves x metres farther away from the stage.

If a bullet from a pistol is fired straight up from the ground, its height t seconds after it is fired will be s (t) = -16t2 + 1280t feet (neglecting air resistance).  a. Find the velocity function b. How long will it take the bullet to fall back to the ground? c. With what velocity will the bullet hit the ground?