How hard must you hit a rod for it to swing up 180 degrees?

In summary, to calculate the necessary velocity to swing a thin rod, the parallel axis theorem must be used to find the correct moment of inertia. The equation for calculating this velocity is P(change in potential energy)=K(change in rotational kinetic energy) = 1/2(I)(Wv)^2, where P is the change in potential energy, K is the change in rotational kinetic energy, I is the moment of inertia, and Wv is the rotational velocity. Other equations that may be helpful in this calculation include P=mgh, I=1/12(mL^2), V(rotational coordinate omega)=s/r, Wv=(Vt (tangential velocity))/r, and Ac (centripetal acceleration)=(V
  • #1
Lauren Wright
2
0

Homework Statement


A thin rod, 0.79 m long, is pivoted such that it hangs vertically from one end. You want to hit the free end of the rod just hard enough to get the rod to swing all the way up and over the pivot.
How fast do you have to make the end go?

Homework Equations


P(change in potential energy)=K(change in rotational kinetic energy) = 1/2(I)(Wv)^2
P=mgh (where h is change in height)
I=1/12(mL^2) (the rotational inertia of a thin rod)
V(rotational coordinate omega)=s/r (where s is distance traveled around circle and r is radius)
Wv(rotational velocity)=(change in V)/(change it time)
Wv=(Vt (tangential velocity))/r
Ac (centripetal acceleration)=(V^2)/r
*the change in height of the thin rod is the change in the center, not the tip
*there could be more but I think I covered everything

The Attempt at a Solution


https://goo.gl/rsq8QO <---- url link to a picture of my work
I know the answer is not 5.56 m/s or 3.78 m/s[/B]
 
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  • #2
Lauren Wright said:
I=1/12(mL^2) (the rotational inertia of a thin rod)

The rod is rotating about one end not the center for which your moment of inertia is for. Do you know the parallel axis theorem?
 

What is the scientific concept behind hitting a rod to make it swing up 180 degrees?

The scientific concept behind hitting a rod to make it swing up 180 degrees is conservation of energy and momentum. When the rod is hit, it stores potential energy which is then converted into kinetic energy as it swings up. The momentum of the rod also plays a role in determining how high it will swing.

What factors affect the force needed to swing a rod up 180 degrees?

The force needed to swing a rod up 180 degrees is affected by several factors, including the mass and length of the rod, the angle at which it is hit, and external forces such as friction and air resistance.

How can we calculate the force required to swing a rod up 180 degrees?

The force required to swing a rod up 180 degrees can be calculated using the equation F = mgL/2sinθ, where F is the force, m is the mass of the rod, g is the acceleration due to gravity, L is the length of the rod, and θ is the angle at which it is hit.

Is there a minimum force needed to swing a rod up 180 degrees?

Yes, there is a minimum force needed to swing a rod up 180 degrees. This force is determined by the mass and length of the rod, and the angle at which it is hit. If the force is below this minimum, the rod will not swing up 180 degrees.

What are some real-life applications of understanding the force needed to swing a rod up 180 degrees?

Understanding the force needed to swing a rod up 180 degrees can have practical applications in fields such as engineering and physics. For example, it can help in designing structures and machines that rely on swinging motion, as well as in predicting the trajectory of objects in motion.

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