St. Vincent College PH : General Physics 1. Exam 5 11/17/2014

Transcription

1 St. Vincent College PH : General Physics 1 Exam 5 11/17/2014 The exam consists of 4 questions. The questions may not be worth the same number of points, so read the entire exam before beginning work. You must show your work in order to get full credit. Problem 1 20 Problem 2 28 Problem 3 27 Problem 4 25 Total 100 v f = v i + at x f x i = v i t + (1/2)at 2 x f x i = (1/2)(v i + v f )t v 2 f = v2 i + 2a(x f x i ) E = cb v = fλ E = hf n = c/v n i p + n t q = n t n i R M = n iq n t p g = 9.8 m/s 2 down 1 inch = 2.54 cm (exact) 1 mile = 5280 feet 1 J = ev 1 lb = N 1 W = 746 hp k e = N m 2 /C 2 ǫ 0 = C 2 /N m 2 µ 0 = 4π 10 7 T m/a e = C Electron m e = kg Proton m p = kg Neutron m n = kg c = m/s G = N m 2 /kg 2 Solid Cylinder or Disc I = (1/2)MR 2 Hollow Cylinder or Hoop I = MR 2 Solid Sphere I = (2/5)MR 2 Spherical Shell I = (2/3)MR 2 Rod about one end I = (1/3)ML 2 Rod about center I = (1/12)ML 2 Radius of Earth r E = m Mass of Earth m E = kg

2 1. (20 pts) a) (5 pts) Why, in the interest of having to walk farther just to hit it again, should one follow through in their swing at a golf ball? (As opposed to checking the swing as soon as the club contacts the ball.) b) (5 pts) A perfectly elastic collision is one in which no kinetic energy is lost, or transferred to other forms of energy. Describe one real-world situation in which the collisions are perfectly elastic. c) (5 pts) A car makes a hard left turn, pinning the passenger against the right side door. What force acting on the passenger causes them to travel in a circle (which force acts as the centripetal force) and in what direction is this force? d) (5 pts) A bunch of grapes of identical size and mass is twirled around the stem, which just happens to go right down the middle of the bunch. Do the grapes on the outer edge of the bunch have more, less, or the same kinetic energy as the grapes near the stem?

3 2. (28 pts) A 30 kg child sits on the edge of a 2.5 m radius disc-shaped merry-go-round, initially at rest. His friend gives the merry-go-round a running start, causing the child to have a final angular speed of 95 per second after running along side and pushing the merry-go-round for 3/4 of one rotation. a) (10 pts) Assuming that it was constant, what was the angular acceleration (in radians/s 2 ) of the merry-go-round? b) (6 pts) What is the (translational) speed of the child once the friend stops pushing the merry-goround? c) (12 pts) What is the minimum coefficient of static friction between the child s pants and the merrygo-round needed to prevent the child from sliding off?

4 3. (27 pts) One section of General Physics decides to ditch the lab assignment for the day and build a snow ball cannon. It shoots 0.8 kg snow balls horizontally at a speed of 150 m/s. a) (10 pts) The students mount the 80 kg cannon on a frictionless sled in the middle of a flat, horizontal area. After the first shot, what is the recoil speed of the cannon? b) (10 pts) The concurrent Organic Chemistry class sees the commotion outside and wants to get in on the winter fun. They build a giant snow man with a head made of 8 kg of packed snow. Unfortunately, they build the snow man directly in the line of fire of the snow ball cannon. One of the snow balls hits the snow man s head and ends up embedded in it. If the head is able to slide off of the abdomen (so-called by the Biology Lab section still inside) without friction, how fast does it move right after the impact? c) (7 pts) How much kinetic energy is lost during this collision?

5 4. (25 pts) A comet in deep space is at rest in a certain inertial frame of reference. When a small space ship of 15 kg mass, from an insignificant planet third in line orbiting a small, yellow dwarf star and on which the people still think digital watches are cool, unceremoniously smashes into it with a speed of 8 m/s in the +x direction, it breaks into three pieces. One piece with 48 kg of mass travels at 16 m/s in the +x direction. A second piece of 62 kg mass travels at 15 m/s at 75 above the negative x direction (i.e. face the x direction and rotate 75 degrees towards the +y direction). The third piece, on which is stuck the crashed space craft, has a mass of 112 kg. With what speed and in what direction does this third piece travel?