Physics TBR tension pendulum motion

[deleted647690]

"What is the tension in the string in trial 4 if the pendulum bob swings through equilibrium with a speed of 4 m/s?"
There is a data table that gives 5 trials of a pendulum swung at different lengths, with trial 4 being at 4 meters and 40.4 seconds for 10 oscillations to occur.

I did this question based on an equation I learned last semester in my physics II class, v0 = square root of T*L/m, but I got 0.4 kg/s^2, which doesn't even make sense in terms of units.

Does anyone recognize the equation I used?

They solved it using an equation, Fnet = mv^2/r, which I do not recognize.

They said that the sum of the forces in the y direction would be T - mg = mv^2/r

Could someone explain what this equation is?

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[deleted647690]

"What is the tension in the string in trial 4 if the pendulum bob swings through equilibrium with a speed of 4 m/s?"
There is a data table that gives 5 trials of a pendulum swung at different lengths, with trial 4 being at 4 meters and 40.4 seconds for 10 oscillations to occur.

I did this question based on an equation I learned last semester in my physics II class, v0 = square root of T*L/m, but I got 0.4 kg/s^2, which doesn't even make sense in terms of units.

Does anyone recognize the equation I used?

They solved it using an equation, Fnet = mv^2/r, which I do not recognize.

They said that the sum of the forces in the y direction would be T - mg = mv^2/r

Could someone explain what this equation is?

The equation I referenced was for the speed of a transverse wave, I guess the pendulum produces a longitudinal wave rather than a transverse wave. I have never seen that other equation before though.

 

[theonlytycrane]

Fnet = mv^2 / r is for uniform circular motion. They are considering the pendulum at the equilibrium position (hanging straight down) where v = 4 m/s and r = 4 m.

 

[deleted647690]

Fnet = mv^2 / r is for uniform circular motion. They are considering the pendulum at the equilibrium position (hanging straight down) where v = 4 m/s and r = 4 m.

Hm, circular motion, would that be related to centripetal force? my physics courses never covered circular motion

 

[NicMouse64]

Hm, circular motion, would that be related to centripetal force? my physics courses never covered circular motion

have you drawn a FBD? The force of gravity, and the tension must be equal and opposite. The Tension in this case is the centripetal force as it is what keeps the object in a circular motion rather than falling straight to the ground. Also the force of gravity is always perpendicular to the tangential velocity of the circular path.