Physics Study Guide Answer Key
1. 25 feet per second (ft/s)
2. Velocity includes speed AND direction (speed is just how fast it travels).
3. Velocity will increase (in the downward direction).
1. Net force: 10 N left
a. Weight and normal force are balanced, so the object does not accelerate in those directions
(speed is not changing – still 0).
b. Applied force and friction are unbalanced, so the object speeds up in the direction of the net
force (in my drawing, to the left).
c. Net force: 10 N to the left. Look to cancel out as many forces as possible (remember,
balanced forces have a net force of 0 N).
d. Yes, because the net force is not 0 N. It will accelerate to the left.
2. All forces are balanced (weight and normal, applied and friction) because the car is moving with a
CONSTANT SPEED. Forces should be labeled with numbers given.
3. This is Newton’s first law – an object at rest stays at rest until an outside force acts on it.
4. Newton’s third law is “for every force, there is an equal and opposing force.” When a box pushes
down on a table, the table pushes back up, resisting the box’s efforts to fall through the table.
1. Kinetic energy depends on mass and velocity (speed). Potential energy depends on mass and
height.
2. The Law of Conservation of Energy says that energy cannot be created or destroyed – it can only
change forms. This means that potential and kinetic energies are always changing back and forth,
but total energy remains constant.
3. Since kinetic energy depends on speed, we would expect the KE to increase (double). Potential
energy does not depend on speed, so PE does not change.
4. The balloon from the second floor starts with more potential energy, since it is higher up (height is a
factor in PE). Since that balloon has more potential energy, it will also have more kinetic energy
(because all energy becomes kinetic just before it hits the ground).
5. All objects fall at the same speed, so their final speeds will be the same, regardless of mass.
6.
7. Sound, chemical, radiant (light), electrical, atomic (nuclear), mechanical, thermal
8. Sound (blender, garbage disposal, etc.), chemical (food, chemicals, etc.), radiant (appliance lights,
windows, etc.), electrical (appliances, lights, etc.), atomic (very rare – present in nuclear devices,
probably not in your kitchen), mechanical (toaster, blender, etc.), thermal (oven, toaster, motors,
etc.)
9. During an energy transformation, energy is always lost as heat (thermal).
10. Chemical (battery)  electrical  sound (jingle), mechanical (vibration), radiant (light)
11. Renewable – is produced or created faster than it is consumed (biomass, wind, solar, etc.)
Non-renewable – is consumed faster than it is created (fossil fuels, uranium)
12. Fossil fuels provide over 70% of the United States’ electrical energy.
13. Concerns: non-renewable, produces pollution, contributes to acid rain, major cause of global
warming
Benefits: cheap, already in use
14. Wind energy
15. Nuclear waste is buried underground in barrels at designated sites. Nuclear energy is nonrenewable and poses multiple safety concerns. Plants are prohibitively expensive to build and
maintain. However, nuclear energy is vastly more efficient than fossil fuels, producing the same
amount of energy of 1780 lb of coal in just 7 g of uranium.
16. Conduction – hand touching the pot handle, convection – circulation of liquids in the pot, radiation –
heat rays coming from the stovetop in all directions
17. Insulator – does not transmit energy (heat) well (wood, plastic, etc.)
Conductor – transmits energy (heat) well (metals)
1. Light travels best through empty space, while sound travels best through matter (specifically highdensity objects like solids). Light travels well in a vacuum, but sound cannot travel at all. Visible
light cannot pass through a thick door, but sound travels through solid doors well.
2. Echoes are caused by sound reflecting off of surfaces.
3. Light travels fastest in gases.
4. Sound travels fastest in solids.
5. See below.
a. Blue
b. Red
c. Orange
6. See below.
a. Everything but purple
b. Everything but green
c. Everything but yellow
7. A pencil looks broken in water because the light has changed speeds. In the air, the light travels
fast. But when the light enters the water, it slows down, changing direction slightly. When it
reenters the light, it speeds up again. That time when the light traveled slowly makes it look like the
pencil is in a different place than it actually is.