# Homework Help: Help with Acceleration problems

1. Nov 3, 2011

### gabez

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.

Last edited: Nov 3, 2011
2. Nov 3, 2011

### PeterO

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.

3. Nov 3, 2011

### Redbelly98

Staff Emeritus
Welcome to Physics Forums.

Actually, it's $a = \frac{\Delta v}{\Delta t}$, right? 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 $a = \frac{\Delta v}{\Delta t}$ ( 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: