What is the power input at time t=3s for the force of 5N on an 8kg object?

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SUMMARY

The discussion focuses on calculating the power input at time t=3s for a force of 5N acting on an 8kg object. The key equations involved include the relationship between power, work, and time, expressed as P=W/t, and the work done calculated using kinetic energy, W=1/2 mv^2. Participants emphasize the need to derive velocity as a function of time using F=ma and relate it to power input over time. The discussion also touches on a car's performance, requiring similar calculations for power and kinetic energy.

PREREQUISITES
  • Newton's Second Law (F=ma)
  • Kinetic Energy Formula (W=1/2 mv^2)
  • Power Calculation (P=W/t)
  • Basic Algebra for solving equations
NEXT STEPS
  • Learn how to derive velocity as a function of time using F=ma
  • Study the relationship between work and power in mechanical systems
  • Explore the concept of constant power and its implications in physics
  • Investigate the effects of time on kinetic energy in accelerating objects
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Students studying physics, particularly those focusing on mechanics, as well as educators and tutors assisting with homework related to force, power, and motion calculations.

nns91
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Homework Statement



1. A single force of 5N acts in the x direction on a 8kg object. (a) If the object starts from rest at x=0 at time t=-, find its velocity v as a function of time. (b) Write an expression for the power input as a function of time. (c) What is the power input of the force at time t=3s

2.A car manufacturer claims that his car can accelertate from frest to 100 km/h in 8s. The car's mass is 800kg.

(a) Assuming that this performance is achieved at constant power, determine the power developed by the car's engine.
(b) What is the car's speed after 4s (neglect friction and air resistance)

Homework Equations



p=W/t


3. The Attempt at a Solution [/b

1. I could not even do part a of number 1. Can you guys help me ?

2. So since it's constant power P=W/t. W can be calculated by 1/2 mv^2 right ?

How can I do part b ? Do I just use the P from previous calculation and multiply by time 4 s to get W. and set W=1/2 mv^2 ??
 
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1a) F = ma gives you the acceleration, use it to find v(t).
1b) With 1a) you can get an expression for the work performed by the force on the object. Relate the work to the power and express p(t).
1c) Use 1b).

2a) You can express the cars kinetic energy at 100 km/h. This energy has been received linearly in time.
2b) You know the kinetic energy given after 4 s from 2a), relate it to velocity.
 
2b. How can I know kinetic energy at 4s ? does the kinetic energy stay the same as in part a ??
 
nns91 said:
2b. How can I know kinetic energy at 4s ? does the kinetic energy stay the same as in part a ??
Well, it differs in time, but it is given linearly according to the problem description, starting at 0 going up to the maximum value after 8 s. From 2a) you can express energy given per time unit which should give you energy given after 4 s.
 
Can I just calculate the acceleration and find velocity from there ?
 
Can I just calculate the acceleration and find velocity from there ?
 

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