Centripetal Acceleration Question

[tdreceiver17]

An object weighing 4 Newtons swings on the end of a string as a simple pendulum. At the bottom the swing, the tension in the string is 6 Newtons. What is the magnitude of the centripetal acceleration of the object at the bottom of the swing.Centripetal Acc. = v^2/r Sum of forces = T+Ac=mg?Attempt

-T-mg=Ac?
-6-4 = Ac
I don't know where to go from here.

 

[vela]

Newton's second law says
$$\sum \vec{F}_i = m\vec{a}.$$ The centripetal acceleration is not a force. It's an acceleration. It goes into the righthand side of F=ma. The tension and the weight go into the lefthand side. Try again and pay attention to the sign of T and mg when summing the forces.

 

[tdreceiver17]

Newton's second law says
$$\sum \vec{F}_i = m\vec{a}.$$ The centripetal acceleration is not a force. It's an acceleration. It goes into the righthand side of F=ma. The tension and the weight go into the lefthand side. Try again and pay attention to the sign of T and mg when summing the forces.

So I set it up as Sum of forces = T-mg=Ac
6-4=Ac
2?

 

[vela]

Closer. The lefthand side is correct, but the righthand side isn't. You can't add up a bunch of forces and then set the result to something that isn't a force. $a_c$ is the centripetal acceleration; it's not a force. It's the $a$ in $ma$ on the righthand side.

 

[tdreceiver17]

Closer. The lefthand side is correct, but the righthand side isn't. You can't add up a bunch of forces and then set the result to something that isn't a force. $a_c$ is the centripetal acceleration; it's not a force. It's the $a$ in $ma$ on the righthand side.

ah my bad I was correcting it as you answered .
so is it 2=mAc
so its 2 g ? the answer choices only come in a number times g

 

[vela]

Not quite. You need to figure out what the mass of the object is from its weight.