physics
posted by Morgan .
I;m sorry, but I was stuck on the second part of this problem. Can you please help me?
An automobile engine slows down from 4500 rpm to 1500 rpm in 2.5 seconds.
a) calculate angular accceleration
b)calculate total number of revolutions done in this time.
What I did:
a) I got the answer, and it was right, and it was also negative, but: what confused me was b
b) It is decelerating, this really confused me. I wasn't even sure how to approach this.

average speed=4500+1500 divided by 2, or
average speed=3000 rpm
displacement=avgspeed*time
=3000rpm or 3000rev/3600sec *2.5sec
= 7500/3600 rev 
I'm sorry, I tried this and got 2.1 and the computer keeps kicking it out as wrong. Your logic makes sense to me after I thought about it. Is there something I'm doing wrong?

wait never mind. There are only 60 seconds in a minute!
Respond to this Question
Similar Questions

physics
A car engine accelerates at a constant rate from 170 rpm to 3050 rpm in 7 seconds. I have found that at t=0, the angular velocity (omega)=17.8 rad/s, the angular acceleration (alpha)= 43.1 rad/s^2, the tangential acceleration = 7.76 … 
physics
I;m sorry, but I was stuck on the second part of this problem. Can you please help me? 
phy
An automobile engine slows down from 3500 rpm to 1100 rpm in 4.5 s. (a) Calculate its angular acceleration, assumed constant. rad/s2 (b) Calculate the total number of revolutions the engine makes in this time. rev I got answer for … 
Physics
During an acceleration, the angular speed of an engine increases from 900 rpm to 2800 rpm in 4.5 s. What is the average angular acceleration of the engine? 
physics
A DVD is spinning at 180 rpm’s. Calculate its angular acceleration when it increases to 240 rpms’s in 2 seconds. (Remember, convert rpm’s to radians/second) 
mechanics
Find the total kinetic energy of a 1500 g wheel, 700 mm in diameter, rolling across a level surface at 650 rpm. Assume that the wheel can be considered as a hoop. (b) For the wheel in part (a), calculate the torque required to decrease … 
PHYSICS
a wheel rotating at 1800 rpm slows down uniformly to 1200 rpm in 2.0 sec. calculate a)the angular acceleration (revs/s^2) of the motor. and b) the number of revolutions it makes in this time. 
Physics
The crankshaft of an engine increases its spin from 1,200 rpm to 1,500 rpm in 0.50 s. What is its angular acceleration 
Physics
The angular velocity of an engine increase from 1200 RPM to 3000 RPM in 10 second computer angular acceleration and the number of revolution made during this time. 
physic
A small fly wheel fitted to a motor with a moment of inertia of 80 kg m² slows down from 9000 rpm to 5500 rpm in 7.5 seconds. For the fly wheel, calculate: • The rate of deceleration which you can assume to be constant • The braking …