TORQUE (Section 8.2)
Stuff you should know!
1)
2)
3)
4)
Describe torque and the factors that determine it.
What is a lever arm and how is it measured?
What is the axis of rotation for a rotating object?
How do you measure the angle θ in order to properly use the equation:
τ = rFsinθ ?
Sample Problems (from Ch 8)
14. You stand on the pedal of a bicycle. If you have a mass of 65kg, the
pedal makes an angle of 35o above the horizontal, and the pedals is
18cm from the center of the chain ring, how much torque would you
exert? (94N*m)
81. A bolt is to be tightened with a torque of 8.0 N*m. If you have a wrench
that is 0.35m long, what is the least amount of force you must exert?
(23N)
3. (pg 227) A child attempts to use a wrench to remove a nut on a bicycle. Removing the nut requires a torque of
10N*m. The maximum force the child is capable of exerting at a 90o angle is 50N. What is the length of the wrench
the child must use to remove the nut? (0.2m)
7. (pg 227) You use a 25-cm long wrench to remove the lug nuts on a car wheel, as shown in the illustration below. If
you pull up on the end of the wrench with a force of 2.0x102N at an angle of 30o, what is the torque on the wrench?
(43N*m)
Illustration for problem 7 above.
CENTER OF MASS AND EQUILIBRIUM (Section 8.3)
Stuff you should know!
1.
2.
3.
4.
5.
6.
What is center of mass? What is the center of mass for commonly found objects?
How does the location of the center of mass affect the stability of an object?
How does the center of mass differ between men and women?
If an irregularly shaped object is thrown into the air (a projectile) then how does its center of mass behave?
What are the “two conditions” for static equilibrium?
How do you choose a pivot point in order to properly calculate rotational equilibrium?
Sample Problems (from Ch 8)
90. Ten bags of topsoil, each weighing 175N, are placed on a 2.43m-long
sheet of wood. They are stacked 0.50m from one end of the sheet of
wood, as shown at right. Two people lift the sheet of wood, one at
each end. Ignoring the weight of the wood, how much force must each
person exert? (Fright = 1400 N, Fleft = 360N)