Exam I
Solutions
Part A. Multiple choice questions. Check the best answer. Each question carries a value of 4 points.
1.
Two projectiles are launched simultaneously with the same speed from the same
spot on the ground, one at 30° elevation and the other at 60°.
They will rise to the same height.
They will reach their maximum height at the same time.
√
They will return to the ground at the same distance.
They will return to the ground at the same time.
2.
A car rounds a curve of radius
R
at constant speed
v
but radial acceleration
a
.
Which of these is wrong?
a
=
v
2
/
R
.
√
The occupants of the car feel a component of their weight toward the
center of the curve. [Away from the center.]
The weight of an occupant of mass
m
is
m
g
2
+
a
2
.
No work is being done on the car.
Physics 53
Summer 2010
1
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
3.
Which of these statements about work, energy and power is true?
Work done by nonconservative forces always decreases the total
energy.
The potential energy of a massspring system is positive if the spring is
compressed but negative if it is stretched.
If two objects acted on by the same force follow the same path, the
power input by the force is the same for both.
√
If an object moves in a closed path the work done by gravity is zero.
4.
A particle is subject to a single conservative force
F
(
x
)
for which the potential
energy is
U
(
x
)
. The total energy is
E
. Which of the following is NOT true?
The particle cannot be found at a point
x
for which
E
<
U
(
x
)
.
√
At a point where
dU
/
dx
>
0
the force
F
(
x
)
>
0
. [
F
(
x
)
=
−
dU
/
dx
.]
At points where
E
=
U
(
x
)
the particle is at least momentarily at rest.
A point where
U
(
x
)
has a minimum is a point of stable equilibrium.
This is the end of the preview.
Sign up
to
access the rest of the document.
 Spring '07
 Mueller
 Physics, Energy, Force, Kinetic Energy, Potential Energy

Click to edit the document details