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. ____27 m/s______

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

Ans. ____37.2 m______

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

Ans._____5.51 s_____


(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 _____9.9 m/s___

direction ___31.8° west of north____


(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. ____4 s___

b) What is the height of the building?

Ans. ____30.4 m____

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 ____16 m/s____

vertical _____27.2 m/s___


(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. ____30.4 N_____

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

Ans.____27.8 N___

c) Calculate the mass m of the second box?

Ans. ____4.0 kg____