# demolition ball, whats the tension in the cable

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• October 29th 2007, 12:42 PM
rcmango
demolition ball, whats the tension in the cable
A 1900 kg demolition ball swings at the end of a 15 m cable on the arc of a vertical circle. At the lowest point of the swing, the ball is moving at a speed of 7.4 m/s. Determine the tension in the cable.

also i know that the tension force has the same purpose as the normal force.

please help me with this one.
• October 29th 2007, 10:15 PM
CaptainBlack
Quote:

Originally Posted by rcmango
A 1900 kg demolition ball swings at the end of a 15 m cable on the arc of a vertical circle. At the lowest point of the swing, the ball is moving at a speed of 7.4 m/s. Determine the tension in the cable.

also i know that the tension force has the same purpose as the normal force.

please help me with this one.

The tension is equal to the sum of the weight ( $mg$) and the force needed to
deflect linear motion into circular motion about the suspension point ( $mv \dot{\theta}$).

RonL
• October 30th 2007, 04:59 AM
topsquark
Quote:

Originally Posted by rcmango
A 1900 kg demolition ball swings at the end of a 15 m cable on the arc of a vertical circle. At the lowest point of the swing, the ball is moving at a speed of 7.4 m/s. Determine the tension in the cable.

also i know that the tension force has the same purpose as the normal force.

please help me with this one.

As usual, the first point of attack on this problem is to sketch a Free-Body Diagram. All of your forces are in the vertical direction, so you only have one direction to consider. Also, as I (I think) have mentioned to you before, the centripetal force is the same as the net force in the radial direction.

So calling the vertical direction the y axis:
$\sum F_y = F_c$

and go from there.

-Dan