Engine block

10. The exhaust manifold on a car engine needs to be replaced. The manifold is held in place by one-fourth-inch diameter steel bolts that pass through holes in the manifold and thread into the cast iron engine block (i.e., the bolts are free to rotate within the holes in the manifold). The “free” length of the bolts (the length not screwed into the engine block) is 4.0 inches. Due to time and exposure to the elements during the operation of the car, the bolts have rusted in the engine block. To try to remove the bolts, a mechanic will apply a force on the end of a 1.0-foot-long wrench handle. The mechanic doesn’t want to break the bolts during the process of trying to remove them, so he did some research and estimated the shear strength of the bolts is 75,000 psi and the shear modulus is G = 11.5 × 10⁶ psi.