Question

Which equation would best help solve the following problem?

fiona releases a javelin 1.2m above the ground with an initial vertical velocity of 20 m/s. how long will it take for the javelin to hit the ground?

A. -4.9t^2+1.2t+20=0
B. -4.9t^2+20t+1.2=0
C. -16t^2+20t+1.2=0
D. -4.9t^2+20t=1.2

Answer 1

Option B:

`-4.9t^2+20t+1.2=0`

General formula for the height(feet) of a projectile over time:

`h(t)=-16t^2+v_0t+h_0`

where h represents height (feet)

t represents time

`v_0` represents initial velocity

`h_0` represents initial height(feet)

General formula for the height(metres) of a projectile over time:

`h(t)=-4.9t^2+v_0t+h_0`

where h represents height (feet)

t represents time

`v_0` represents initial velocity

`h_0` represents initial height(metres)

Given data in the question:

`h_0=1.2` metre

`v_0=20` m/s

To determine the equation to find time:

Substitute
`h_0` and
`v_0` in general formula for the height(metres) of a projectile over time:

`h(t)=-4.9t^2+20t+1.2`

`\Rightarrow -4.9t^2+20t+1.2=0`

Therefore option B is the correct answer.

`-4.9t^2+20t+1.2=0`