Chapter 11

Torques

When you pedal a bicycle you exert a torque, The length of the crank arm is important for people who race bicycles. The crank arm length is the distance from the center of the crank axle to the center of the pedal axle. The torque you apply is impacted by the amount of force you can apply, the length of the crank arm and where you are in your stroke.

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1. A 100 cm meter stick is balanced at its center  point (that is, at the 50 cm point). If a weight of 10 N is hanged from the 30 cm mark and a weight of 20 N is hanged from its 60 cm mark, find out whether the meter rule will remain balanced about its pivot or not?

2. A child of mass 20 kg is located 2.5 m from the fulcrum or pivot point of a seesaw. Where must a child of mass 30 kg sit on the seesaw in order to provide balance?

3. Two girls are sitting on the same side of a see-saw.  Mandy is 28 kg and is 2.4 m away from the middle. Sandy is 35 kg and is 2.6 m away from the middle.  Their dad can balance them out if he  sits 2.0 m away from the middle on the other side. What is the mass of the dad?

4. Calculate the magnitude of the torque in each of the cases below. The force F is 40 N and the length L is 0.2 m.

5. While painting the side of a large building, Francie decides to take a break on the scaffolding. The board of the scaffold has a mass of 20kg and is 3 m long. Francie sits 1.2 m away from the right side of the scaffold and the automatic tension meter in the rope near her reads 340N.

a) What is the tension in the other rope?

b) What is Francie’s weight?

Any man who can drive safely while kissing a pretty girl is simply not giving the kiss the

attention it deserves.

Albert Einstein

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7. A construction crane balances its load by using a counterweight.  Ned, the crane operator can slide the entire torque arm horizontally in order to balance the load.  The arm is 56 m long. The arm has a mass of 750kg.  The counterweight has a mass of 2,500 kg.  If he wants to balance a load of 860kg, where should Ned position the pivot point?

For each of the following find the unknowns:

8.

9.

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