- #1

GiantYoda

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- Homework Statement
- If a projectile's initial vertical velocity is 12.5 m/s. What is the time it takes in the air till it reaches the same horizontal level, neglecting air resistance?

Note: I know how it can be solved, but I am asking why can't I use the following kinematic equations?

Δy=[(vyi+vyf)/2]*Δt

- Relevant Equations
- Kinematic equations

Givens:

Vyi=12.5 m/s

Vyf=-12.5 m/s (at the same horizontal level)

ay=-9.81 m/s^2

Δy= zero m (as the displacement on the y-axis, when the projectile reaches the same horizontal level, is zero m)

Δt=?

When I use

Δy=[(vyi+vyf)/2]*Δt

I get the time as undefined.

Δt= 2Δy/(vyi+vyf)

= 2*0 m/(12.5 m/s +-12.5 m/s)

Any reason why can't I use this specific kinematic equation?

Vyi=12.5 m/s

Vyf=-12.5 m/s (at the same horizontal level)

ay=-9.81 m/s^2

Δy= zero m (as the displacement on the y-axis, when the projectile reaches the same horizontal level, is zero m)

Δt=?

When I use

Δy=[(vyi+vyf)/2]*Δt

I get the time as undefined.

Δt= 2Δy/(vyi+vyf)

= 2*0 m/(12.5 m/s +-12.5 m/s)

Any reason why can't I use this specific kinematic equation?