# Homework Help: Is this the correct formula that im using for this question?

1. Apr 15, 2007

### ImsoFly

1. The problem statement, all variables and given/known data
hi this is the problem: the burning of the second stage of a two stage toy rocket takes the rocket from 12 m/s to 40 m/s in 5.0s. How far does the rocket during this time?

2. Relevant equations
would i use delta t= delta v/a ? would the given info be.. delta v1= 17 m/s, delta v2=40m/s and delta t=5.0s... if this isnt the correct formula please correct me. thank u all!

2. Apr 15, 2007

### misterme09

distance = (1/2)*a*t^2 + vi*t

where a = delta v / delta t

and vi is the initial velocity (12 m/s)

3. Apr 15, 2007

### ImsoFly

but the question asks for time

4. Apr 15, 2007

### cristo

Staff Emeritus
No it doesnt.. it asks for distance! Firstly, work out the acceleration using your equation, then plug this along with initial velocity and time into the equation for distance given in post #2.

5. Apr 15, 2007

### ImsoFly

what do you mean by working out the acceleration?

6. Apr 15, 2007

### cristo

Staff Emeritus
sorry, you'll just be going round in circles by doing that! you can use another of the "kinematic equations", namely $$d=\frac{v_i+v_f}{2}\cdot t$$.

Here's a link to the kinematic equations http://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/1DKin/U1L6a.html [Broken]. These equations are normally the tools you need for questions involving a constant acceleration.

Last edited by a moderator: May 2, 2017
7. Apr 15, 2007

### ImsoFly

kk, thanks a bunch:tongue2:

Last edited by a moderator: May 2, 2017
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