Calculating Instantaneous Power in a Uniformly Accelerating System

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In summary, the conversation is about finding the instantaneous power delivered by the net force to a car that is accelerating uniformly from rest to a speed of 17.1 m/s in 4.21 seconds. The equation for power is P=dw/dt, which is equal to the product of force and velocity. The speaker uses the equations vf=vi+at and F=ma to find the acceleration, which is then used to calculate the net force and ultimately, the power. However, there is some confusion about whether the final velocity or the initial velocity should be used in the power equation. The speaker is reminded that the final velocity should be used and suggests using kinematics to find the speed at 2 seconds.
  • #1
lonely86driver
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i need a little help on this problem and I'm not sure if i have the equation down right.

a 1990kg car accelerates uniformly fromrest to a speed of 17.1 m/s in 4.21 sec.
now the question states what is the instantaneous power delivered by the net force to the car at 2s. answer in units of w.

so this is what i did.
i know that the equation is P=dw/dt which is F*v
to find F i did F=ma but i need to find out what a is
vf=vi+at

vf=vi+at
17.1m/s = 0 m/s + a(2s)
a = 8.55 m/s

F = 1990kg (8.55m/s) = 17014.5

then i plug all that into P= F*v
P = 17014.5 * 17.1 m/s = 290947.95

but that's wrong (online submit). my instructor told the class that v in that equation is the final velocity. am i doing something wrong here. i already found the average power in for the 4.21s and i already found work done.
 
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  • #2
You need to find the speed at 2s, then multiply it by the net force.
 
  • #3
how would i find speed? isn't speed change of x over change of time?
 
  • #4
You know the acceleration is uniform and it stars from rest, Kinematics? :smile:
 

1. What is instantaneous power?

Instantaneous power is the amount of power being used or produced at a specific moment in time. It is often measured in watts (W) and is a measure of how quickly energy is being transferred.

2. How is instantaneous power different from average power?

Instantaneous power refers to the power at a specific moment, while average power is the total amount of power used or produced over a period of time. Average power takes into account fluctuations in instantaneous power over time.

3. What causes instantaneous power problems?

Instantaneous power problems can be caused by a variety of factors, such as changes in energy demand, equipment malfunctions, or power grid disruptions. These issues can result in spikes or drops in instantaneous power that can lead to power outages or damage to electrical systems.

4. How can instantaneous power problems be prevented?

To prevent instantaneous power problems, it is important to have a well-maintained and properly designed electrical system. This includes regularly inspecting and maintaining equipment, using surge protectors, and having a backup power source in case of emergencies.

5. What are the potential consequences of instantaneous power problems?

Instantaneous power problems can have a range of consequences, from minor inconveniences such as flickering lights to more serious issues like equipment damage or power outages. These problems can also result in financial losses for businesses and safety hazards for individuals.

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