HighFour Physics
Category C: Grades 9 - 10
Round 6
Monday, Feburary 20, 2017
The use of calculator is required.
Answer #1:
Solution:
647 Hz
The source of the sound is Martin’s trombone. Since Martin is moving
with his sports car, then the source of the sound is moving as well.
Hence, we can use the following formula to solve for the frequency as
received by the concrete:
(
(
Answer #2:
Solution:
)(
)
297000 Pa
The total amount of pressure is given by the pressure of the air plus the
pressure to change in elevation. The formula can be found in Table 3 of
the Physics Data Booklet.
(
Answer #3:
Solution:
)
)(
)(
)
37.8 kg
The density of glycerin can be found in Table 8 of the Physics Data
Booklet. The volume on the other hand, can be obtained by multiplying
the length, width and height of the aquarium.
(
)(
)
HighFour Physics
Category C: Grades 9 - 10
Round 6
Monday, Feburary 20, 2017
The use of calculator is required.
Answer #4:
Solution:
84 375 J
Solve for the speed of the truck first, using the formula for kinetic energy:
√
√
(
)
If the speed is halved, it will be equal to 15 m/s. Hence,
(
)(
)
Answer #5:
Solution:
- 150 m
The car moved 250 m east, then 400 m west. Hence, the displacement is
given by
(
)
Answer #6:
Solution:
- 4.8 cm
By sign convention, the focal length of a convex mirror is negative. Using
the Mirror Equation:
Image formed is always virtual for a convex mirror, thus the negative
sign.
Answer #7:
Solution:
6.125
The formula for Actual Mechanical is found in Table 3 of the Physics Data
Booklet. Output force is given by the hanging weight.
(
)(
)
HighFour Physics
Category C: Grades 9 - 10
Round 6
Monday, Feburary 20, 2017
The use of calculator is required.
Answer #8:
Solution:
118 m
If air resistance is absent, then the sum of the potential energy and the
kinetic energy is constant at any point. Hence, potential and kinetic
energy will be equal halfway the height of N Seoul Tower, hence, 118 m.
Answer #9:
Solution:
8 cm
The given sinusoidal graphs are a displacement vs time graph and a
displacement vs distance graph. Of the two, the wavelength can be
easily read from the displacement vs distance graph. This is given by the
distance over which the wave’s shape repeats – that is, the distance
between two successive crests, troughs, or similar points on the graph.
Answer #10:
Solution:
361°C
The formula relating the speed of sound in air and temperature is given
in Table 3 of the Physics Data Booklet. It is stated in the problem that the
temperature is raised by 30° so the new temperature value is 50°C.
(
Answer #11:
Solution:
)
19.8°
We are only concerned with the
water-oil interface as shown in the
figure on the right:
Snell’s law can be found in Table 3 of the Physics Data Booklet, and we
are looking for the value of .
(
)
HighFour Physics
Category C: Grades 9 - 10
Round 6
Monday, Feburary 20, 2017
The use of calculator is required.
Answer #12:
Solution:
41°
The force applied on the crate, assuming friction is negligible, is equal to
the tension on the string. Work is given by the following formula:
Solving for θ,
(
Answer #13:
Solution:
(
(
)
)( )
12
Using the formula provided, solve for the number of images formed for
each angle α, then then get the difference. A smaller angle will have
more images formed than a larger angle, due to greater instances of
reflection, so:
(
Answer #15:
Explanation:
)
9.8 s
We are given the values of the distance, acceleration and initial speed
and are asked to solve for the time elapsed. We may use the UAM
(Uniformly Accelerated Motion) formula found in Table 3 of the Physics
Data Booklet.
( )
Answer #14:
Solution:
)(
) (
)
52°
Complementary angles, or angles with sum of 90°, will produce the same
range for a projectile. The complementary of 38° is 52°.
HighFour Physics
Category C: Grades 9 - 10
Round 6
Monday, Feburary 20, 2017
The use of calculator is required.
Answer #16:
Solution:
97.85 km/h
The average speed is given by total distance divided by the total time.
The given values are summarised as follows:
We need to calculate the time for the travel from Alpha to Beta, as well
as the distance from Beta to Charlie. Once these values are obtained,
we can compute the average speed for the entire travel.
From Alpha to Beta:
From Beta to Charlie:
(
)(
)
Solving for the average speed:
Answer #17:
Solution:
55°
A detailed diagram of the path of light ray is shown below.
Remember that the angles of incidence and reflection are always
measured from the normal. Also, the sum of angles inside a triangle is
180°.
HighFour Physics
Category C: Grades 9 - 10
Round 6
Monday, Feburary 20, 2017
The use of calculator is required.
Answer #18:
Solution:
- 3.75 cm
For a concave lens, the focal length is negative. The formula that relates
the focal length, object distance and image distance for mirrors and
lenses are the same, so we can use the formula provided in Table 3 of
the Physics Data Booklet. Solving for v:
The image distance is negative, meaning the image is virtual or found on
the same side of the lens as the object.
Answer #19:
Solution:
1002 kJ
For a change in phase from solid to liquid and vice versa, we can use the
given value for latent heat of fusion of water. To solve the amount of
heat energy needed to melt the ice and assuming that there is no
change in temperature (phase change only), we multiply the mass by the
latent heat.
(
Answer #20:
Solution:
)(
)
27.1 m/s
The stone is undergoing projectile motion and the final velocity can be
obtained from its final horizontal and vertical components. The stone is
projected horizontally from the top of the cliff, and hence its horizontal
velocity is constant. For the vertical component, we may use the formula:
√( )
)(
(
) √
Again, the final velocity can be calculated from the resolution of the xand y-components.
√(
)
(
)