Why Doesn't My Power Calculation Match Real-World Scenarios?

  • Thread starter Thread starter Aeronautician
  • Start date Start date
  • Tags Tags
    Accelerate Power
Click For Summary

Homework Help Overview

The discussion revolves around calculating the power required for a motor to accelerate a mass of 1633 kg over a distance of 2 meters in 1 second. The original poster expresses confusion over a significant discrepancy between their calculated power output and a reference scenario involving a 215 hp propulsion system for a different mass.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the original poster's calculation of acceleration and power, questioning the assumptions made regarding constant acceleration and power. Some suggest using kinematic equations and differentiating between average and maximum power. Others inquire about the nature of the motor's power output, including whether it is constant or varies with velocity.

Discussion Status

The discussion is ongoing, with participants providing various perspectives on the problem. Some have offered insights into the nature of power calculations and the implications of constant versus variable acceleration. Clarification is sought regarding the motor's characteristics, indicating a productive exploration of the topic.

Contextual Notes

There is a noted ambiguity regarding the assumptions about the motor's power output and the conditions under which the calculations are made. The original poster's reference scenario involves a significantly different mass and power requirement, which raises questions about the applicability of their calculations.

Aeronautician
Messages
2
Reaction score
0

Homework Statement


Hi, guys. I'm in a bit of a quandary. I'm trying to calculate the power a motor should have in order to move a mass a certain distance. My calculation keeps telling me that the horsepower output is much lower than my reference scenario. Here's the situation. I'm trying to figure out how to accelerate a 1633 kg object a distance of 2 m in 1 sec.
m = 1633 kg
d = 2 meters
t = 1 sec

Homework Equations


F=ma
P=F(d/t)

The Attempt at a Solution


Acceleration is thus 2 m/(s^2). According to F=ma, F = 3266 Newtons. Plugging this into P=F(d/t), where d=2m, t=1 sec, Power needed = 6532 Watts or approx 8.8 hp. The problem is in a similar situation, a 215 hp propulsion system is needed to provide the thrust to accelerate and sustain a mass of 95 kg above ground. Where is this discrepancy coming from? My calculations clearly do not correlate with the already established real world scenario. Can I get some direction in this issue?
 
Physics news on Phys.org
Use the kinematic motion equations
to solve for acceleration. Your formula for power yields average power, not max power at the 2 meter mark
 
  • Like
Likes   Reactions: Zachary Kempler
+1. The required acceleration is not 2m/s^2.

If the acceleration is constant the power isn't constant and the max power will occur at max velocity.
 
Aeronautician said:
trying to calculate the power a motor should have
Turning around the preceding responses, your situation is constant power, so not constant acceleration.
The SUVAT equations will therefore not apply. You need to work instead with the more general differential forms.
Work done in time t ##=Pt=\frac 12 mv^2##. Can you solve to find position as a function of time?
 
Perhaps we need the OP to clarify...

Does the motor generate a constant power? Does it have a power vs velocity or rpm curve?
 

Similar threads

  • · Replies 25 ·
Replies
25
Views
2K
  • · Replies 42 ·
2
Replies
42
Views
6K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 41 ·
2
Replies
41
Views
6K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 3 ·
Replies
3
Views
3K
  • · Replies 8 ·
Replies
8
Views
3K
  • · Replies 13 ·
Replies
13
Views
4K
Replies
7
Views
2K
  • · Replies 20 ·
Replies
20
Views
2K