Gravitational and kinetic energy problem

Click For Summary

Homework Help Overview

The problem involves calculating the total frictional force acting on an automobile moving at a constant velocity of 72.8 mi/h, given the power output of the engine in horsepower and its conversion to watts. The context includes concepts of gravitational and kinetic energy, as well as the relationship between power, force, and velocity.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss converting power from horsepower to watts and velocity from miles per hour to meters per second. There is an exploration of the relationship between power, force, and velocity, with attempts to express force in terms of these quantities. Questions arise regarding the necessity of certain variables, such as time and mass, and how to handle multiple unknowns.

Discussion Status

Participants have engaged in a back-and-forth discussion, clarifying the relationships between the quantities involved. Some have proposed equations and substitutions, while others have confirmed understanding of the concepts. There is acknowledgment of the force provided by the engine and its relation to the frictional force at constant velocity, although no explicit consensus on the final answer is reached.

Contextual Notes

Participants note the absence of specific values for the mass of the car and displacement, which are relevant to the problem but not provided in the statement. The discussion reflects an understanding of the implications of constant velocity on acceleration and force balance.

lzh
Messages
109
Reaction score
0

Homework Statement


Given: 1 hp = 746 W and 1 m/s =2.237 mi/h.
When an automobile moves with constant
velocity, the power developed in a certain en-
gine is 85.4 hp.
What total frictional force acts on the car
at v = 72.8 mi/h? Answer in units of N.


Homework Equations


Kinetic Energy=.5mv^2
Disspated energy=F*displacement <-the f would be the frictional force.
W=change in energy(J)/change in time(s)

The Attempt at a Solution


i first converted 85.4 hp to W: 63708.4W
then the v to m/s: 32.54m/s

i would like to find the amount of joules in 63708.4W, but I don't know the time. So I probably need to find a way to cancel it.

also, I don't know the mass of the car...nor the displacement. I'm not sure of what to do with so many unknowns.
Can someone point my problems out?
Ty in advance!
 
Physics news on Phys.org
Why should you want joules for??

Instead, how are the quantities power, force and velocity related?
 
power=Force*displacement/time
after some simplification
I'm starting to see something though
edit:i forgot to type /t
 
Last edited:
You have constant velocity. What is therefore displacement/time equal to?
 
Last edited:
velocity!
i see, ty
 
so that means Force*v=63708W
substituting v i get:
F=1957.84N
but that's not the frictional force, I'm going to solve for that next
 
So, what you have found is the force the engine provides on the system, agreed?

Now, how much acceleration does the car experience if it moves with constant velocity?
 
yeah that's the force of the engine.
car at constand velocity has 0 accelaeration
so at constant velocity, the force of friction must be equal to force of engine?
so F=1957.84N is correct?
 
Last edited:
Correct!:smile:
 
  • #10
ty!
it was correct, according to my utexas's homework service
 
  • #11
lzh said:
ty!
it was correct, according to my utexas's homework service

How fortunate for the homework service! :smile:
 

Similar threads

How Is Potential Energy Converted to Kinetic Energy in Physical Systems?
  • · Replies 6 ·
Replies
6
Views
1K
Falling stick problem (no friction): What is the kinetic energy?
  • · Replies 3 ·
Replies
3
Views
2K
Conservation of Momentum Problem - Mechanical and Kinetic Energies
  • · Replies 2 ·
Replies
2
Views
1K
Resistance force changing the velocity of an object
  • · Replies 8 ·
Replies
8
Views
2K
Finding the final speed of a space probe using work and kinetic energy
  • · Replies 7 ·
Replies
7
Views
2K
Solving the Platform and Object Kinetic Energy Equation
  • · Replies 8 ·
Replies
8
Views
2K
Lifting an object, kinetic energy, work and forces
  • · Replies 11 ·
Replies
11
Views
6K
Kinetic energy & Conservation of energy
  • · Replies 17 ·
Replies
17
Views
2K
Kinetic Energy and Newton Forces - distance/speed
  • · Replies 3 ·
Replies
3
Views
2K
Need help with finding thermal and Kinetic energy
  • · Replies 20 ·
Replies
20
Views
2K