PSS 8.1: Static equilibrium problems Learning Goal: To practice Problem-Solving
ID: 1325487 • Letter: P
Question
PSS 8.1: Static equilibrium problems
Learning Goal:
To practice Problem-Solving Strategy 8.1 Static equilibrium problems.
When you lift an object by moving only your forearm, the main lifting muscle in your arm is the biceps. Suppose the mass of a forearm is 1.50kg . If the biceps is connected to the forearm a distance dbiceps = 3.50cmfrom the elbow, how much force Fbiceps must the biceps exert to hold a 750g ball at the end of the forearm at distance dball = 37.0cm from the elbow, with the forearm parallel to the floor? How much force Felbowmust the elbow exert? (Figure 1)
What is the horizontal distance d forearm between the elbow and the point where the weight of the forearm acts?
Explanation / Answer
Given that,
mass of the forearm = m = 1.5 kg
dbicep =l = 3.50 cm = 0.035m
Mass of the ball = M = 750 g = 0.75 kg
dball =L= 37 cm = 0.37 m
Lets write an eqn for all the acting forces,
l.F(bicep) -1/2Lmg - LMg = 0
Solving the above eqn for F(bicep), we get
F(bicep) = { (1/2m + M ) Lg } / l = { (1/2x1.5kg + 0.75kg) 0.37 m x 9.8 m/sec2 } / 0.035 m
F(bicep) = 155.4 N
For calculating F(elbow)
L.F(elbow) - l F(bicep) -1/2 Lmg - LMg = 0, we get
F(elbow) = { lF(bicep) + Lg (1/2m + M) } / L = { (0.035 x 155.4 )+ 0.37 x 9.8 (1/2x1.5 + 0.75 ) } / 0.37
F(elbow) = 29.4 N
d(forearm) = 1/2L = 0.185 m
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.