Acceleration and Speed Equations?

Question

I noticed that there are two equations for speed and three for acceleration:

Speed:

1. Speed= distance/time

2.Average Speed= distance covered/time interval

How do I know which ones to use when solving a speed problem?

Acceleration:

1. A=change in velocity/time interval

2. A=change in speed/time interval

3. A=net force/mass

When solving an acceleration problem, how would I know which equation to use?

Please keep the explanations simple and add examples in necessary.

Thank you!!

Answer 1

It sound like you're very new to doing physics problems. What you need is a paradigm for working problems. Here's what I do when answering questions in this forum.

First, and foremost, identify the physics involved. In HS physics there are just a few options: conservation of momentum, conserations of energy, and Newton's laws of gravity and motion. So learn to recognize what physics you are dealing with first. [In this case, you are dealing with Newton's laws of motion.]

Second, put down everything you know about the problem. For example, if it's asking for distance (S), write down all the distance bearing equations you can think of. S = vt and v^2 = u^2 + 2aS, for instance, are two popular distance carryiing equations. They are some of the so-called SUVAT equations you should be intimately familiar with in HS physics. S is distance, U is initial velocity, V is final velocity, A is acceleration, and T is time.

Finally, look at the equations to identify what's missing in value and, of course, which factor is the variable you are trying to solve (like acceleration a). For example, you are looking for acceleration, set up the last equation as a = (v^2 - u^2)/2S and now you know you need to have the two velocities and a distance to solve for a. If one or more of these factors are missing, you must come up with additional relationships or equations with them in them. Once you've found the v, u, and S, just plug them in to solve for a.

Bottom line:

ID the physics first.
Write all the equations you can about that line of physics.
ID the variable you are looking for and rewrite the equations so the variable (like a) is on the LHS of the = sign.
ID what missing from the RHS of the = sign; and solve for those missing values using additional equation as needed.

Answer 2

Speed Acceleration Formula

Answer 3

the 2 measures of speed are exactly the same. the complication comes lower down where you have to distinguish between velocity and speed. the difference here relates to movement in a straight line. You always know which equation to use because the clues are in the question

Answer 4

ok find the total height from the top of the jump to the water level: 3.6m + 1m = 4.6m now use this equation to first find the time: v^2 = u^2 + 2as s is the distance/height(m) u is the initial velocity(m/s) a is acceleration(9.8m/s^2) t is the time(secs) v is the final velocity(m/s) initial velocity is zero since you are starting at rest(at the top) v^2 = u^2 + 2as v^2 = 0^2 + 2(9.8)4.6 v^2 = 90.16 v = 9.5m/s hope you get it^^ hope you get it^^