Phys 1L03 Tutorial session Set 8
Eight series: Questions on Torque and equilibrium
1. trap door, of length and width 1.65 m, is held open at an angle of 65.0 with
respect to the floor. A rope is attached to the raised edge of the door and
fastened to the wall behind the door in such a position that the rope pulls
perpendicularly to the trap door. If the mass of the trap the trap door is 16.8 kg,
what is the torque exerted on the trap door by the rope?
2. A rod is being used as a lever as shown. The fulcrum is 1.2 m from the load
and 2.4 m from the applied force. If the mass of the load is 20.0 kg, what
force must be applied to lift the load?
3. A weight of 1200 N rests on a lever at a point 0.50 m from a support. On the
same side of the support, at a distance of 3.0 m from it, an upward force with
magnitude F is applied. Neglect the weight of the board itself. If the system is
in equilibrium, what is F?
Solve this problem considering the weight of board is 250 N. (Do it at
4. Figure shows a forearm holding a book.
a. Calculate the force the biceps muscle must exerts to hold
the forearm and the book.
b. Compare this force with the weight of the forearm plus its
load, the book.
c. Calculate the force at the elbow joint, FE.
Take the data in the figure to be accurate to three digits.
5. Even when the head is held erect, as shown, its center of mass is not
directly over the principal point of support. The muscles in the back of
the neck must exert a force to keep it upright. That is why your head
falls forward when you fall asleep in class.
a. Calculate the force exerted by these muscles using the
information in the figure.
b. What is the force on the pivot?
6. A 75.0 kg man stands on his toes by exerting an upward force through the
Achilles tendon, as shown.
a. What is the force in the Achilles tendon if he stands on one foot?
b. Calculate the force at the pivot of the simplified lever system shown –
that force is representative of forces in the ankle joint. 7. What force must the wind exert to keep the chicken from falling over
in the image below if the chicken has a mss of 2.50 kg? What is the
ratio of this force to the chicken’s weight?
8. A woman whose weight is w = 500 N is poised at the right end of a diving board with a length of