College of Applied Medical Sciences Biomedical Technology Department Biomechanics BMT 228 First Semester 1422-1423 Final Exam

Student Name ___________________________________Student Number ___________________________________

DR. Saleh AL-Tayyar 17/10/1422

Question 1. Answer the following :a) A weight lifter bench-presses a 1000 N barbell as shown. He begins the lift with his arms extended and the barbell 75 cm above his chest. The lifter then lowers the barbell and stops it when it is 5 cm above the chest. He pauses there and then lifts the barbell upward away from his chest and back to the original starting position 75 cm above his chest. The average force exerted by the lifter while raising the weight is also 1000 N.

i) how much work did the lifter do on the barbell during the raising of the barbell?ii) how much work did the lifter do on the barbell during the lowering of the barbell?iii) how much work did the lifter do on the barbell from the start until the finish of the lift?iv) what was the weight lifter’s average power output during the raising of the barbell if only 0.5 sec elapsed from the movement of the barbell until it was 75 cm above his chest?

b) Answer the following with true (T) or false (F).

1) In translational motion, the point of the body describe concentric circles around the axex.

____2) Kinetic is the study of the characteristic of motion. ____3) Friction force acts normal to the direction of motion. ____4) Lubricants are used to minimize interaction between surfaces. ____5) Rectangular components of a force are greater in magnitude than theoriginal force. ____

6) Mechanical advantage provides good estimate of forces acting on a lever system. ____7) Rotational equilibrium occurs when M point = 0 ____8) Bone is strongest in tension. ____

Question 2. Answer the following questions.a) Find the flexing torque (M) on the hip joint when a patient passively stretches the hamstring muscles by flexing the upper body as far as possible in a sitting position.

b) Find the force (P) needed to begin upward sliding a 100 N box up a 60 inclined plane. Assume the coefficient of static friction = 0.20

Question 3. Tendon forces Ta and Tb are exerted on the patella. The femur exerts force F on the patella. If the magnitude of Tb is 80 N, what are the magnitudes of Ta and F, If no motion is occurring at the joint?

Question 4. A 35 N hand and forearm are held at 45 angle to the vertically oriented humerus. The cg of the forearm and hand is located at a distance of 15 cm from the joint center at the elbow, and the elbow flexor muscles attach at an average distance of 3 cm from the joint center. (Assume that the muscles attach at an angle of 45 to the bone) a) how much force must be exerted by the forearm flexors to maintain this position?b) how much force must the forearm flexors exert if a 50 N weight is held in the hand at a distance along the arm of 25 cm?

Bonus Question.Why does a force directed through the axis of rotation not cause a rotation?