1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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?


    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?


    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


    User Avatar
    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


    User Avatar
    Staff Emeritus
    Science Advisor
    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:

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook