Physics 201 MWF10:20 Fall 1999 (Ford)

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


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


(3pts) 1. Object A is projected horizontally with speed v₀ at a height h above the ground. At the same instant object B is released from rest at the same height. Air resistance can be neglected.

a)  A hits the ground before B
b)  B hits the ground before A
c)  both objects hit the ground at the same time


(3 pts) 2. A glass of water rests on a piece of paper that is on a horizontal tabletop. You grab the paper and pull it, causing it to accelerate to the right. While the glass of water is still on the piece of paper, which statement about the friction force f on the glass of water is correct:

a)  f is to the right
b)  f is to the left
c)  f = 0


(4 pts) 3. Three swimmers can swim equally fast relative to the water. They have a race to see who can swim across a river in the least time. Swimmer A swims upstream at an angle to the current and lands on the far shore directly opposite the starting point. Swimmer B swims downstream at an angle to the current. Swimmer C swims perpendicular to the current and lands on the shore far downstream, because the current has swept him in that direction. Who crosses the river in the least time:

a)  A
b)  B
c)  C


(6 pts) 4. The path of a projectile launched on level ground is shown in the sketch. Point A is just after the projectile is launched, point E is just before it hits the ground, and point C is at the maximum height. At points B and D the object is at one-half its maximum height. Air resistance may be neglected.

At which point is the velocity of the projectile perpendicular to its acceleration:

a)  A
b)  B
c)  C
d)  D
e)  E
f)  none of these


At which point is the acceleration zero:

a)  A
b)  B
c)  C
d)  D
e)  E
f)  none of these


(4pts) 5. A traffic light of weight W is suspended from two wires as shown. Then tensions in the wires have magnitudes T₁ and T₂, as shown.

Which statement is true:

a)  T₁ = T₂ = W
b)  T₁ = T₂ = W/2
c)  T₁ + T₂ = W
d)  T₁ + T₂ > W


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


(21 pts) 6. A ball is thrown straight up from the edge of the roof of a building with an initial speed v₀. Air resistance can be neglected. The ball has a speed of 32 m/s just before it strikes the ground.

a) It is observed that the ball reaches a maximum height of 19.6 m above the roof of the building. What was the initial speed v₀ of the ball?

Ans. ___________________________

b) How much time elapses from when the ball was thrown to when it strikes the ground?

Ans. ____________________________

c) What is the height of the building?

Ans. _____________________________


(20 pts) 7. A rock is thrown horizontally from the edge of the roof of a building and lands on the edge of the roof of another building. The spot where the rock lands is a horizontal distance of 16.0 m from where it was thrown.

a) What is the vertical distance from where the rock was thrown to where it lands?

Ans. _________________________

b) What is the magnitude of the velocity of the rock just before it lands on the second roof?

Ans. __________________________


(21 pts) 8. A block suspended from a rope is connected to a block of mass 5.0 kg that sits on a table. The rope and the frictionless pulley have negligible mass. The system is released from rest, the hanging block descends, and while the blocks are moving the tension in the rope is observed to be 25 N. The coefficient of kinetic friction between the block and the table is 0.40.

a) What is the magnitude of the acceleration of the 5.0 kg block?

Ans. _____________________

b) What is the mass m of the hanging block?

Ans. _____________________


(18 pts) 9. An oceanliner is heading due north with a speed of 6.0 m/s relative to the water. Relative to the passengers on the oceanliner a sailboat is traveling due west at a speed of 12.0 m/s. Consider the velocity of the sailboat relative to the water.

a) Write a vector addition equation that shows how the three relative velocities in this problem are related.

b) Draw a clearly labeled vector addition diagram that shows the vector addition of part (a).

c) What is the velocity (magnitude and direction) of the sailboat relative to the water? Show the direction of the velocity of the sailboat relative to the water in a clearly labeled diagram.

Ans. magnitude ____________________

direction ___________________