Physics 207w, w2 (Summer) Exam 1


June 24, 1999
LAST NAME: ___________________________________________________________________________________________________ FIRST NAME: __________________________________________________________________________________________________ Recitation Section: ______________________________________________________________________________________________

General Instruction

You have 1 hour to answer 4 questions on this exam. Work each problem only on the sheet provided for this problem, using the back if necessary. Please write the name and recitation section on each sheet at the top of the page.

You must indicate the reasoning and show all the steps.

If you are unable to obtain the answer to part of a problem and you need the answer to solve the subsequent parts, use an appropriate symbol for the answer to the previous part and solve in terms of that symbol.

Take the following in the exam:

2 g = 10m/s x - x0 = v0t + 1/2at2 v = v0 + at v2 - v20 = 2a(x - x0)

1. A 10kg block is at rest on an inclined plane. The plane is inclined at an angle of 30o from the horizontal direction.
(a) Draw the free body diagram for the block.
(b) Find the normal force and friction on the block.
(c) What is the minimum friction coefficient between the block and the plane?
(25 points)

2. A diving board 3.0m long is supported at a point 1.0m from the end, and the diver weighting 600N stands at the free end. The diving board is of uniform cross section and weighs 300N.
(a) Draw the free body diagram for the board.
(b) Find the force at the supporting point.
(c) Find the force at the end that is held down.
(25 points) PIC

3. A rock is thrown into the air from the roof with an initial velocity 10m/s and an angle 37o above the horizontal direction. The roof is 50m above the ground (ignoring air resistance).
(a) Find the maximum height reached by the rock.
(b) Find the time elapsed before rock hitting the ground.
(c) How far will the rock travel horizontally before hitting the ground?
(d) Find the velocity of the rock just prior to hitting the ground.
(25 points)

4. Atwood machine is one experiment method to measure the gravity. An astronaut wants to measure the gravity of an unknown planet using this method. He hangs a mass M = 101g on one side of the pulley and another mass m = 99g on the other side. He releases the heavier mass at rest h = 1m above the ground and finds it takes 5s for the heavier mass to hit the ground. Assume the pulley is frictionless and has no mass.
(a) Draw the free body diagrams for the two masses.
(b) Find the acceleration of the heavier mass just prior to hitting the ground.
(c) Find the gravity on the unknown planet.
(25 points)