Find the potential gravitational and kinetic energy of a ball after 0.4 seconds

AI Thread Summary
To find the potential gravitational and kinetic energy of a 3.0 kg metal ball after falling for 0.4 seconds, the initial height of 3.5 m must be adjusted based on the distance fallen during that time. The potential energy (PE) is calculated using the height at 0.4 seconds, which is less than 3.5 m due to the fall. The kinetic energy (KE) requires the speed of the ball after 0.4 seconds, which can be determined using kinematic equations. The initial calculations provided were incorrect as they used the initial height and acceleration instead of the actual height and velocity after the fall. Understanding the effects of time on both potential and kinetic energy is crucial for accurate calculations.
Darth Poison
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Homework Statement



A 3.0 kg metal ball is held 3.5m above the ground. Find the potential gravitational and kinetic energy of the ball after it is let go and has fallen for 0.4s


Homework Equations



EK= 1/2mv^2

EP=mgh



The Attempt at a Solution



Okay I know how to find both the kinetic and potential energy, but how does the time effect it? Is there a certain equation I have to sub it in other than the ones given. Please help :)

Potential= EP=mgh
Ep=(3.0Kg)(9.8m/s^2)(3.5m)
EP= 102.9 J

Kinetic = EK=1/2mv^2
EK=1/2(3.0kg)(9.8m/s^2)
EK=14.7 J
 
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Darth Poison said:

Homework Statement



A 3.0 kg metal ball is held 3.5m above the ground. Find the potential gravitational and kinetic energy of the ball after it is let go and has fallen for 0.4s


Homework Equations



EK= 1/2mv^2

EP=mgh



The Attempt at a Solution



Okay I know how to find both the kinetic and potential energy, but how does the time effect it? Is there a certain equation I have to sub it in other than the ones given. Please help :)

Potential= EP=mgh
Ep=(3.0Kg)(9.8m/s^2)(3.5m)
EP= 102.9 J

Kinetic = EK=1/2mv^2
EK=1/2(3.0kg)(9.8m/s^2)
EK=14.7 J

It would seem you actually don't know how to find KE.

You have substituted an acceleration value in for the velocity.

The 0.4 seconds is there as in that time the object will have fallen some distance [so you won't use 3.5 in the PE formula], and will have gained some speed - the value of which you will use in the KE formula.

Normal kinematics for falling objects is used to find the distance and speed values.
 


PeterO said:
It would seem you actually don't know how to find KE.

You have substituted an acceleration value in for the velocity.

The 0.4 seconds is there as in that time the object will have fallen some distance [so you won't use 3.5 in the PE formula], and will have gained some speed - the value of which you will use in the KE formula.

Normal kinematics for falling objects is used to find the distance and speed values.



Thank you for helping me realize that, I appreciate it. :D
 

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