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Homework Help: Help with Acceleration problems

  1. Nov 3, 2011 #1
    Show all work using LESSS to answer questions 1 - 3.

    1. A car starts from rest and proceeds west, accelerating to a velocity of 100 km/h in exactly one minute. What was the acceleration in m/s2?

    a=ΔvΔt

    This is what I got for #1
    L Delta A = ?
    E Delta A = Ai= 27.8m/s Af= 60 seconds
    S Delta A = Ai/Af = 27.8 / 60 =
    S Delta A = 0.463
    S Delta A = 0.5m/s2


    2. A car traveling north at 50 m/s speeds up to 80 m/s by accelerating at a rate of 4.0 m/s2. What was the time required?

    T= Iv/fv*a?

    3. A plane traveling at 200 km/h north accelerates at 5.00 m/s2 for two minutes. What is the planes final velocity in m/s?

    Final velocity = iv+ t * a


    3. A plane traveling at 200 km/h north accelerates at 5.00 m/s2 for two minutes. What is the planes final velocity in m/s?

    Final velocity = (Initial velocity) + (time)(acceleration)



    Show your work including equation, substitution and final answer, for questions 4 – 7.

    4. A boy on a bicycle travels in a straight line east and slows down from 30 m/s to 10 m/s in 5.0 s. What is his acceleration?

    a=ΔivΔfv


    5. A car travelling south slows down from 80 m/s to 40 m/s by accelerating at -4.0 m/s2. What time interval was required?

    Time = Initial Speed/Final Speed*Acceleration?


    6. A car travelling south accelerates at 3.0 m/s2 for 9.0 s and reaches a speed of 90 m/s. What was the car’s original speed?

    Not sure


    7. A car traveling east at an unknown speed applies the brakes and slows down at a rate of 5.0 m/s2 for 5.0 s. If the final velocity of the car is 95 m/s east, what was the original velocity of the car?

    Not sure

    I'm aware I need to at least try, Which i'm doing now.
    Thanks in advance.
     
    Last edited: Nov 3, 2011
  2. jcsd
  3. Nov 3, 2011 #2

    PeterO

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    Homework Helper

    What on Earth does LESSS mean?

    1: do you know how to convert km to metres? hours to seconds? minutes to seconds?
    because the acceleration is obviously 100km/hour/minute - it is just a unit conversion from there.

    All the other questions are a fancy way of asking "Do you know what acceleration is/means?"

    You are indicating the answer is no.
    All these examples seem to be in a straight line, which makes things simpler.
    If you accelerate at 5 m/s2 for 3 seconds, you velocity will increase by 15 m/s.

    If it was 12, it will now be 27.

    If it becomes 35, it was originally 20.

    hope that helps.
     
  4. Nov 3, 2011 #3

    Redbelly98

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    Homework Helper

    Welcome to Physics Forums.

    Actually, it's [itex]a = \frac{\Delta v}{\Delta t}[/itex], right? :wink: Let's call this Useful Equation #1.

    That's the correct answer. But I have no idea what LESSS means, and you seem to be using "Delta A" to mean both the initial velocity and the acceleration, which are different things.

    No, use [itex]a = \frac{\Delta v}{\Delta t}[/itex] ( Useful Equation #1) as before. You are given a and you can figure out what Δv is from the given information.

    That is the correct equation. Let's call it Useful Equation #2. Plug in the given information and calculate it -- you'll need to do some units conversions.

    What does Δiv even mean here? The change in the initial velocity? That doesn't even make sense.

    Instead, try using either Useful Equation #1 or Useful Equation #2. In fact, all the remaining problems can be solved using either Useful Equation #1 or Useful Equation #2:

     
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