- #1

aatari

- 71

- 3

## Homework Statement

Problem: [/B]During a pond hockey game, a puck accelerates from rest at 5.0 m/s 2over a distance of 80.0 cm. The puck then slides with a constant speed for 4.0 s until it reaches a rough section which causes it to stop in 2.5 s.

**a.**What is the speed of the object when it reaches the rough section?

## Homework Equations

[/B]

*a*= (

*v*

_{2}−

*v*

_{1}) / Δ

*t.....*

**(1)**Δ

*d*=

*v*

_{1}Δ

*t*+ ½

*a*Δ

*t*

^{2}...

**(2)**

Δ

*d*= (

*v*

_{2}

^{2 }−

*v*

_{1}

^{2}) / 2

*a...*

v

**(3)**v

_{2}=

*v*

_{1}+

*a*Δ

*t......*

**(4)***v*_{2}^{2}=*v*_{1}^{2}+ 2*a*Δ*d...***(5)**## The Attempt at a Solution

Hi guys, I know how to solve this question but I am having trouble understanding when to use which equation. And I am hoping one you can help me understand when to use what equation.

So for the question above we are asked to find the speed of the puck, which is very easy. The way I understand, we can solve this by either using equation (4) or equation (5). Both these equations will give us the final velocity. However, if I use equation 4 my answer is 20 m/s and if I use equation 5, I get 2.8 m/s. This is a significant difference and I don't understand why this is.

How do I figure out when to use what equation in situation like this?