NAME ______________________
PH125-001
Exam 1a
Feb. 13, 2012
Part 1. Enter your answers to this part on the scan sheet.
1. A ball is thrown straight up into the air with an initial speed of 8 m/s. How high does it go?
(Neglect air resistance.)
(a) 3.3 m (b) 4.5 m (c) 5.1 m (d) 6.3 m (e) 8 m
2. A truck pushes a small car up a hill with increasing speed. The force that the truck exerts on the
car is
(a)
(b)
(c)
(d)
greater than the force the car exerts on the truck.
less than the force the car exerts on the truck.
the same as the force the car exerts on the truck.
Need more information to decide which is greater.
3. A man stands on a scale. According to Newton’s 3rd law, the reaction to the gravitational force
acting on the man is
(a)
(b)
(c)
(d)
(e)
the scale pushing up on the man.
the man pushing down on the scale.
the man pulling up on the earth.
the scale pushing down on the floor.
the floor pushing up on the scale.
4. A ball is thrown straight up into the air. Air resistance cannot be neglected. Which is true?
(a)
(b)
(c)
(d)
(e)
The magnitude of the acceleration going up is greater than coming down.
The magnitude of the acceleration going up is less than coming down.
The return speed is greater than the release speed.
The return speed is the same as the release speed.
None of the above is true.
5. The direction of the acceleration of a car rounding a curve is shown.
Which statement is definitely true.
(a)
(b)
(c)
(d)
(e)
The car is going to the right.
The car is going to the left.
The car is speeding up.
The car is slowing down.
None of the above statements are definitely true.
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a
6. The velocity of an object is given as a function of time below.
v (m/s)
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0
t (s)
2
4
6
8
-5
What is the displacement of the object from 0 to 8 seconds?
(a) 20 m (b) 10 m (c) -10 m (d) -5 m (e) 0 m
7. An object is subjected to two forces, as shown. What is the
magnitude its acceleration (in m/s2)? Neglect gravity.
F2 (8 N)
=
o
20
y
(a) 5.2 (b) 6.2 (c) 9 (d) 1 (e) 9.8
F1 (10 N)
x
m = 2 kg
8. A block hangs by a cord from the ceiling of an elevator that is descending at a constant speed.
Compared to the tension when the elevator is at rest, the tension in the cord while descending is
(a) larger (b) smaller (c) the same (d) dependent on the speed of the elevator
9. A 2000-N force is required to pull a car up a 15o hill. If friction is negligible, what is the mass
of the car?
(a) 210 kg (b) 5070 kg (c) 2000 kg (d) 790 kg (e) 520 kg
10. A projectile can be fired from the edge of a cliff at three
different angles with the same speed, as shown. Which results
in the greatest speed upon impact with the ground? (Neglect
air resistance.)
(a) 1 (b) 2 (c) 3 (d) same for all (e) need more information
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1
2
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Part 2. Show your answers to this part in the space provided (required for credit). .
1. A projectile is fired from ground level with a speed of 50 m/s at an angle of 35o above the
ground and hits a building 200 m away. Neglect air resistance.
(a) How long was the projectile in flight before hitting the building?
t = ________ s
(b) How high above the ground did it hit the building?
h = ________ m
(c) What was the speed of the projectile just before it hit the building?
v= ________ m/s
(d) Was it rising or falling when it hit the building? Justify your answer.
2. A block of mass m is pulled along a rough, flat surface with a rope at an angle  above the
surface. The coefficient of kinetic friction between the block and surface is µk.
(a) Draw a free-body diagram showing
all the forces acting on the block.
(b) Starting with Newton’s 2nd law, derive an expression for the normal force, n, in terms of m,
g, , and the tension in the rope, F.
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(c) Likewise, derive an expression for the acceleration of the block in terms of m, g, , µk, and
F.
(d) Now, assuming that F is constant, determine the angle for which the acceleration is a
maximum.
3. Two blocks are tied together by a light rope over a light, frictionless pulley as shown. Given m1
= 5 kg, m2 = 8 kg, and µk = 0.3 (between mass 2 and the surface).
1
2
2
1
2
2
(a) Draw a free-body diagram for each block separately in the space above.
(b) Calculate the acceleration of the blocks.
a = ________ m/s2
(c) Calculate the tension, T, in the connecting rope.
T = ________ N
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4. Joe driving his car at 25 m/s passes Mary who is driving her car at a constant 10 m/s. At the
moment they are side-by-side, Joe immediately applies brakes and decelerates at 2 m/s2 until
Mary catches up with Joe.
(a) On a single graph, plot Joe and
Mary’s position as a function of
time until Mary catches up with Joe.
(b) How long does it take for Mary to catch back up with Joe?
t = ________ s
(c) How far do they travel during this time?
t = ________ s
(d) At what time are they both going at the same speed?
t = ________ s
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