A rock is tossed vertically from a height of 2m with an initial velocity of 20 ms-1. The height of the rock, h, after t seconds can be modeled by the polynomial function :h(t)=−4.9t2+20t+2, t≥0. Calculate how many seconds, rounded to three significant figures, it takes for the rock to hit the ground.

The rock takes 4.18 seconds to hit the ground

Step-by-step explanation:

Function Model

The height of a rock h, after t seconds, can be modeled by the polynomial function:

When the rock hits the ground, the height is 0, thus we need to find the value of t such as:

A quadratic equation can be expressed as:

where a,b, and c are constants.

Solving with the quadratic formula:

The values for the given equation are:

a=-4.9, b=20, c=2

Applying the formula:

There are two possible solutions:

Since t > 0, the only solution is t=4.19 seconds

The rock takes 4.18 seconds to hit the ground

step-by-step explanation:

given perimeter: 28cm

length: 9cm

atp,

2(l+w)=p of the reactangle

2(9+x)=28

18+2x=28

2x=28-18

x=10/2

x=5

therefore width is 5 cm