You are driving at a reasonable constant velocity in a van with a windshield tilted 120∘ relative to the horizontal (Figure 1) As you pass under a utility worker fixing a power line, his wallet falls onto the windshield. Assume the coefficient of static friction between the glass and the wallet to be 0.55.

Question: Determine the acceleration needed by the van so that the wallet stays in place.

What is the length x of the side of the triangle below? (hint: use the cosine function)

Consider an ordinary, helium-filled party balloon with a volume of 2.2 ft3. the lifting force on the balloon due to the outside air is the net resultant of the pressure distribution exerted on the exterior surface of the balloon. using this fact, we can derive archimedes’ principle, namely that the upward force on the balloon is equal to the weight of the air displaced by the balloon. assuming that the balloon is at sea level, where the air density is 0.002377 slug/ft3, calculate the maximum weight that can be lifted by the balloon. note: the molecular weight of air is 28.8 and that of helium is 4.

Which of these has some mechanical energy? a. an atom b. heat inside earth c. a book on a shelf d. the fire from a lit match