View Full Version : Acceleration calculation - what am I doing wrong?

Solfe

2012-Mar-24, 06:33 PM

I am trying to figure out how to use the formula for calculating acceleration.

First try:

Initial speed - 0 metres/s^2

Final speed - 100 metres/s^2

Time - 10 seconds.

Answer - 10 meters/s^2

Follow up question: How many g's is 10 meters/s^2?

Answer is 10 meters/s^2/9.8 meters/s^2= 1.0204 g's.

Second try:

Initial speed - 0 metres/s^2

Final speed - 1,000,000 metres/s^2 (1,000 KM)

Time - 1000 seconds.

Answer - 1000 meters/s^2

Follow up question: How many g's is 1000 meters/s^2?

Answer is 1000 meters/s^2/s^2/9.8 meters/s^2 =102.04 g's.

Am I doing this correctly?

Something "feels" wrong about this and I have no idea what it could be.

Gsquare

2012-Mar-24, 07:17 PM

appears to be correct Solfe...

Rememebr to always start with the formula and simply plug in the knowns and solve for the unknown.

V(f) - V(i) = at

100 m/sec - 0 = (a)(10 sec)

Now solve for a.

:)

grapes

2012-Mar-24, 07:33 PM

Final speed - 100 metres/s^2

::snip::

Am I doing this correctly?

Something "feels" wrong about this and I have no idea what it could be.Maybe it's the speed in metres/s^2 instead of metres/s :)

Solfe

2012-Mar-24, 07:37 PM

Maybe it's the speed in metres/s^2 instead of metres/s :)

I was doing this on paper, so I think you are right. I was writing the wrong terms.

I will get the hang of this someday. :)

Extracelestial

2012-Mar-25, 03:26 PM

I am trying to figure out how to use the formula for calculating acceleration.

First try:

Initial speed - 0 metres/s^2

Final speed - 100 metres/s^2

Time - 10 seconds.

Answer - 10 meters/s^2

Follow up question: How many g's is 10 meters/s^2?

Answer is 10 meters/s^2/9.8 meters/s^2= 1.0204 g's.

Second try:

Initial speed - 0 metres/s^2

Final speed - 1,000,000 metres/s^2 (1,000 KM)

Time - 1000 seconds.

Answer - 1000 meters/s^2

Follow up question: How many g's is 1000 meters/s^2?

Answer is 1000 meters/s^2/s^2/9.8 meters/s^2 =102.04 g's.

Am I doing this correctly?

Something "feels" wrong about this and I have no idea what it could be.

Hello Solfe,

there's a wrong unit in your initial variables:

#1 Speed (i.e. velocity) is expressed in distance per time. E.g Miles per hour or metres per second (m/s). Accelerations, i.e. change of velocity over time, is therefore expressed as distance per times squared: (m/s^2)

#2 As acceleration is change of velocity over time one can write: a = v/t. Solving for v this yields : v = a*t. So simply multiply your acceleration with time and you'll get your final speed.

Ex

P.S.

A more general equation is a = ^v/^t. Acceleration equals change of velocity in a certain tie period. Therefore: a = (v2-v1)/(t2-t1)

profloater

2012-Mar-25, 03:54 PM

Or in distance terms v^2 = u^2 + 2.a.s where a is acceleration and s distance in consistent units. u is the starting speed.

the link from distance to time is s= u.t + 1/2. a.t^2

Ivan Viehoff

2012-Mar-26, 12:39 PM

FYI, you are dealing with constant accelerations. Whilst motion under gravity tends to have constant acceleration, mechanical devices like cars tend not to have constand accelrations.

So a sports car that does 0-60mph in 5 seconds has a average acceleration of about 12mph per second (a rather mixed unit, but it helps understand the principle), in practice its accleration will not be constant, and the distance it travels will not be precisely half-a-t-squared.

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