Question

If an object is projected upward with an initial velocity of 123 ft per​ sec, its height h after t seconds is h=−16t2+123t. Find the height of the object after 5 seconds.

Answer 1

Height after 5 seconds is 215 ft

Explanation:

Given that:

The initial velocity of object which is projected upwards is 123 ft/sec.

Height of the object, h after time t in seconds, is given as:

`h=-16t^2+123t`

Here, t will always be positive, so
`123t` and
`16t^2` will also be positive.

But coefficient of
`16t^2` is negative, that means something is subtracted from the positive term
`123t`.

To find:

Height of object after 5 seconds.

Solution:

Given that
`t=5` seconds.

Let us put the value in the given relation of
`h` and
`t`:

`h=-16* 5^2+123 * 5\\\Rightarrow h=-400+615\\\Rightarrow \bold{h = 215\ ft}`

So, height after 5 seconds is 215 ft.