Physics—Forces
(True or False)
When an object has balanced forces acting on it (net force = 0), there is no change in the object's motion.
True. Balanced forces are forces that cancel each other out (see p. 227)
Energy can be defined as the ability to do work.
True. Energy is the ability to do work.
(True or False)
A transverse wave is a wave in which the medium vibrates at right angles to the direction the wave travels.
True. A transverse wave is a wave in which the medium vibrates at right angles to the direction the wave travels.
BONUS (+300): Draw a wave and correctly label the following parts: amplitude, crest, trough, wavelength.
Generally speaking, how do we see things?
The reason we see things is that reflects off of them and enters our eyes. Our eyes then detect the light and send signals to the brain, which forms an image in our mind.
If wavelength increases, frequency ______.
If wavelength increases, frequency decreases. They are inversely proportional.
(True or False)
Static friction is friction that opposes motion once the motion has already started.
Kinetic friction is friction that opposes the initiation of motion.
False.
Static friction opposes the initiation of motion, and kinetic friction opposes motion once the motion has already started.
A 1,200 kg car is traveling at a speed of 24 m/s. How much kinetic energy does the car have?
KE = 1/2 x m x v2
KE = 0.5 x 1200 kg x (24 m/s)2 = 345,600 kg x m x m/s x s
(True or False)
Surface waves are waves in which the vibration of the medium is parallel to the direction the wave travels.
Longitudinal waves are waves that travel along the surface of the medium.
False.
Surface waves are waves that travel along the surface of the medium.
Longitudinal waves are waves in which the vibration of the medium is parallel to the direction the wave travels.
(True or False) Polarized light is light waves that vibrate in only one plane.
True. Polarized light is light waves that vibrate in only one plane (usually in the horizontal plane).
If I sit on a table with a force of 100 N and the table does not break, what force is the table exerting on me? Is the net force balanced or unbalanced?
The table exerts an equal force of 100 N. Because I am not going through the table or bouncing off the table, we say that the forces (of me to the table and the table to me) are balanced.
A change in which of the following affects the weight of an object?
a) air resistance
b) friction
c) acceleration due to gravity
d) velocity
A change in c) acceleration due to gravity affects the weight of an object.
If the speed of an object doubles, what happens to its kinetic energy?
KE = 1/2 x m x v2
If the speed of an object doubles, its kinetic energy quadruples.
What kind of waves are sound waves?
a) transverse waves
b) surface waves
c) longitudinal waves
d) quantum mechanical I'msosmart waves
Sound waves are longitudinal waves.
Draw light refracting through a converging lens. (Hint* converging lenses have a convex shape)
(I will judge the drawing(s))
The sides of a converging lens are curved outward (toward the middle)
What is the Doppler effect?
(I will judge the answer(s))
A change in sound frequency caused by the motion of the sound source, motion of the listener, or both?
For every action force there is a
a) friction force
b) net force
c) unbalanced force
d) reaction force
For every action force there is a d) reaction force.
What is the energy of motion called?
What is the energy that is stored as a result of position or shape called?
Energy of motion is kinetic energy.
Energy stored as a result of position or shape is potential energy.
If waves carry energy through a medium, why is there no sound in space?
There is no air in space, and therefore no medium through which a sound wave can travel. Because of this, space is "silent".
What kind of lens do our human eyes have?
When light enters the pupil, it is focused by a converging lens.
What is the relationship between pitch, sound, and frequency?
(I will judge the answer(s))
Pitch is an indication of how high or low a sound is, which is primarily determined by the frequency of the sound wave.
Sound waves with low pitch have low frequency.
Sound waves with high pitch have high frequency.
A physics student climbs a tree. To measure how high she has climbed, she drops a rock and times its fall. It takes 1.3 seconds for the rock to hit the ground. How many feet has she climbed?
d = 1/2 x a x t2
acceleration due to gravity = 32ft/s2
d = 0.5 x 32ft/s2 x (7s)2 = 27.04 ft
Work (Work = force x distance) is done when two conditions are met. (1) An object must move, and (2) a force must be acting on the object in the direction of its motion.
In which of the following is no work done?
a) climbing stairs, b) pushing a shopping cart
c) lifting a rock, d) work is done in all options
d) work is done in each circumstance because the force and motion are in the same direction.
One end of a rope is vibrated to produce a wave with a wavelength of 1.2 meters. The frequency of the wave is 3.3 hertz. What is the speed of the wave in m/s?
v = λ x f
Hertz (Hz) = 1/s
v = (1.2 m)(3.3 1/s) = 3.96 m/s
Where is light focused onto in the human eye, and what kinds of conditions can a poor focusing of this light lead to?
The light is focused by a converging lens onto the retina. In nearsightedness (myopia) the light is focused in front of the retina, not on the retina. In farsightedness (hyperopia) the light is focused behind the retina,, not on the retina.
(I will judge the answer(s))
The greenhouse effect is the process by which certain gases (principally water vapor, carbon dioxide, and methane) trap heat that radiates from earth.
If there is an excess in the amount of these gases, then the earth's atmosphere will get warmer.