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What happens when two forces act in the same direction?
A. They cancel each other out.
b. The stronger one prevails
c. Their strengths are added.
d. Their sum divided by two is the total force.
C. Their strengths are added.
a. force
b.acceleration
c.velocity
d.inertia
c. velocity
To reverse the direction of current in a motor, current is conducted
a. through the armature
b.in the direction of rotation
c. through the brushes to the commutator
d.through the commutator to the armature
c. through the brushes to the commutator
When a wire with a current is placed in a magnetic field,
a. kinetic energy is transformed into potential energy
b. electrical energy is transformed into sound and light
c. electrical energy is transformed into mechanical energy
d. solar energy is transformed into light and heat
c. electrical energy is transformed into mechanical energy
Which formula is used to calculate momentum?
a. Momentum = mass x speed
b. momentum = weight x speed
c momentum = volume x velocity
d. momentum = mass x velocity
d. momentum = mass x velocity
The greater the mass of an object...
a. the easier the object starts moving
b. the greater its inertia
c. the more balanced it is
d. the more space it takes upb. the greater its inertia
According to Newtons third law of motion, when a hammer strikes and exerts force on a nail, the nail...
a. creates a friction with the hammer
b. disappears into the woods
c. exerts an equal and opposite force on the hammer
d. moves at a constant speed
c. exerts an equal and opposite force on the hammer
You can increase the strength of an electromagnet's field by
a. decreasing the current in the solenoid
b. decreasing the number of loops in the solenoid
c. using a stronger ferromagnetic material for the core
d. winding the coils more loosely
c. using a stronger ferromagnetic material for the core
An electric motor uses an electric current to turn
a. pointer
b. brush
c. axle
d. wheel
c. axle
a. in the absence of greatest velocity
b. in the presence of least velocity
c. in the absence of outside forces
d. in the presence of outside forces
c. in the absence of outside forces
The law of universal gravitation states that any two objects in the universe have mass, without exception...
a. attract each other
b.repel each other
c.combine to provide a balanced force
d. create friction
a. attract each other
Magnetic field lines around a bar magnet
a. are only perpendicular to the magnet
b. spread out from one pole and curve around to the other
c. cross back and forth over one another
d. are perfectly straightb. spread out from one pole and curve around to the other
a. stay the same
b. switch to point south
c. change
d.return to zero
c. change
Both solenoids and electromagnets produce magnetic fields using
a. electric current and coiled wires
b. compasses and magnetic fields
c. coiled wires and a ferromagnetic core
d. electric current and a battery
a. electric current and coiled wires
The state that exists when the only force acting on an object is gravity is called
a. free fall
b. inertia
c. acceleration
d. momentum
a. free fall
According to the law of conservation of momentum, when two objects collide in the absence of outside forces...
a. velocity decreases
b. velocity increase
c. the objects have the same momentum before and after they collide
d. the objects have more momentum after they collide than they did before
c. the objects have the same momentum before and after they collide
What is one difference between a galvanometer and an electric motor?
a. an electric motor causes something to move
b. a galvanometer uses an electric current
c. in a electric motor, the armature spins continously
d. an electric motor uses electric energy
c. in a electric motor, the armature spins continously
A step-up transformer is a transformer that increases ___________________
voltage
Which moving object, in all likelihood, will have the greatest momentum?
a. volleyball hit by a fourth- grader
b. volleyball hit by Coach Lewis
c. volleyball hit by an Olympic volleyball player
d. volleyball hit by Coach Lee
c. volleyball hit by an Olympic volleyball player
a. sliding friction occurs
b. static friction occurs.
c. rolling friction occurs
d. fluid friction occurs
c. rolling friction occurs
According to Newton's third law of motion, the strength of a reaction force is ___________________ the strength of the action force.
What is equal to?
Why don't action-reaction forces cancel out?
Forces may cancel out only if they are acting on the same object. Action and reaction forces act on different objects.
How are step-up and step-down transformers used in the transmission of electric current from the electric company to homes?
Step- up transformers are used to increase the voltage of an electric current before it is sent out over transmission lines from the electric company. Step- down transformers decrease the voltage of the current to go through homes and businesses.
On the moon, you weigh about one-sixth of what you wigh on earth. On jupiter you would weigh more than twice your weight on earth. Why?
Weight is the measure of the force of gravity of an object. the more mass results in a stronger gravitational pull. The moon has less mass that earth whereas Jupiter has more mass than Earth.
Explain the interaction of gravity and inertia in maintaining the orbital motion of the planets.
The sun's gravity is what keeps the planets from flying into space, just as the ravity of the planets keeps their moons from flying off. Inertia is the tendency of an object to resist a change in motion. The mass of the planets is great enough that their inertia keeps the in orbit, instead of being pulled into the sun.