Physics 201 MWF10:20 Fall 2002 (Ford)

Exam I Chapts 1--4 Cutnell and Johnson 5th ed


Multiple Choice questions. Circle the correct answer. No work needs to be shown.

(5 pts) 1. A motorboat travels across a river that is 180 m wide. The boat's velocity relative to the water has magnitude 15 m/s and makes an angle of 37° with the bank, in the downstream direction. The current in the river is 5 m/s. How long does it take the boat to cross the river?


(a) 6 s
(b) 9 s
(c) 12 s
(d) 15 s
(e) 20 s
(f) 25 s


(4 pts) 2. A rock is thrown from ground level with a speed of 20 m/s at an angle of 53°. What is the speed of the rock when it is at its maximum height?

(a) 0
(b) 10 m/s
(c) 12 m/s
(d) 16 m/s
(e) 20 m/s


(5 pts) 3. Forces F_A and F_B are the only forces that act on an object that has mass 5 kg. F_A has direction to the east and magnitude 18 N. F_B has direction to the west. What is the magnitude of F_B if the object's acceleration is 2 m/s² to the east?

(a) zero
(b) 3 N
(c) 8 N
(d) 28 N
(e) 33 N
(f) 36 N


(4 pts) 4. A rock is thrown straight up from the ground. When the rock is 20 m above the ground and is traveling upward with a speed of 12 m/s, the acceleration of the rock is

(a) zero
(b) 9.8 m/s², upward
(c) 9.8 m/s², downward
(d) 12 m/s², upward
(e) 12 m/s², downward


(4 pts) 5. A book slides off the edge of a horizontal table with a velocity as it leaves the table that is horizontal and has magnitude 12 m/s. The table top is 4 m above the floor. At the same instant that the book leaves the table, a baseball is released from rest at a height of 4 m above the floor. If air resistance is neglected, which statement is true:

(a) the book reaches the ground before the baseball
(b) the baseball reaches the ground before the book
(c) the book and the baseball reach the ground at the same time


On the following four problems show all your work. Partial credit will be given if earned. Write your answers in the blanks provided.


(20 pts) 6. A person standing next to a building throws a rock straight up from the ground with an initial speed v₀. On its way up, the rock has a speed of 16 m/s when it passes a window ledge 24 m above the ground. Air resistance can be neglected.

a) Calculate the initial speed v₀.

Ans. __________________

b) What is the maximum height above the ground reached by the rock?

Ans. _________________

c) How long after it is thrown does the rock return to the ground?

Ans._________________


(18 pts) 7. Jean, a hockey player, is skating due east at a speed of 6.0 m/s relative to the ice. A teammate passes the puck to him. Relative to Jean, the puck has a speed of 14.0 m/s and is moving in a direction of 37° north of west. What are the magnitude and direction of the puck's velocity relative to the ice? (You must show the direction of this velocity in a sketch that shows the north, south, east and west directions and you must clearly show on the sketch the angle that you give as your answer.)

Ans. magnitude _________________

direction ____________________


(20 pts) 8. A rock is thrown from the roof of a building with a speed of 20 m/s at an angle of 37° above the horizontal. The rock strikes the ground a horizontal distance of 64 m from the base of the building. Air resistance can be neglected.

a) How long is the rock in the air?
Ans. _________________

b) What is the height of the building?

Ans. _________________

c) What are the magnitudes of the horizontal and vertical components of the velocity of the rock just before it strikes the ground?

Ans. horizontal ________________

vertical ___________________


(20 pts) 9. Two boxes are on a horizontal surface. The boxes are connected by a light, horizontal rope. The first box has mass 8 kg and the other has mass m. A person pulls on the first box with a force P = 80 N that is directed 37° above the horizontal and the two boxes accelerate to the right with a = 3.0 m/s². The coefficient of kinetic friction between the boxes and the surface is 0.4.


a) Calculate the normal force that the surface exerts on the 8 kg box.

Ans. ____________________

b) While the boxes are moving, what is the tension T in the rope connecting the boxes?

Ans.___________________

c) Calculate the mass m of the second box?

Ans. _________________