Physics Homework
A uniform electric field has a magnitude of 10 N/C and is directed upward. A charge brought into the field experiences a force of 2.0 N upward. The charge must be
+0.2 C
If a charge of -3 x 10-6 C were allowed to fall through a potential difference of +500 V, the change in potential energy for the charge would be
-1.5 × 10^-3 Joules
Two long bar magnets are aligned so that north poles face each other. The magnets are separated by 1 cm, and a repulsive force between the north poles is 0.04 N. When the separation is increased to 2 cm the force will be
0.010 N
A bullet is fired horizontally at a target 20 m away. The velocity of the bullet as it leaves the gun is 200 m/s. How much, approximately, will the bullet drop on its way to the target?
0.05 m
The mass of an apple on the Earth is 0.2 kg. On the Moon, the mass of the same apple would b
0.2 kg
A ball is projected upward with an initial velocity of 10 m/s. It will reach its maximum height in approximately:
1.0 s
A cyclist races around a circular track at the constant speed of 20 m/s. The radius of the track is40 m. The centripetal acceleration of the cyclist is
10 m/s2, toward the center of the track
A parachutist jumping from an airplane reaches a terminal velocity when the force of air resistance is980 N. The mass of the parachutist is
100 kg
The south pole of a bar magnet is moved toward a short helical coil of wire (solenoid) along the axis of the coil. The coil has 100 turns and the ends of the coil are connected to form a closed circuit. If the coil is replaced with a single loop of the same type of wire, and the magnet is moved exactly as before, the current induced in the loop is
100 times smaller
Two equal charges repel one another with a force of 4.0 × 10-4 N when they are 10 cm apart. (Coulomb's constant is k=9.0 × 109 N.m2/C2.) If they are moved until the separation is 5 cm, the repulsive force will be
16 x 10^-4 N
Suppose you throw a ball vertically downward with a speed of 10 m/s. Neglecting air resistance, what would be the speed of the ball one second later?
19.8 m/s
A capacitor consisting of two parallel plates separated by 2.0 cm has a potential of 40 V on the top plate and a potential of 0 V on the bottom plate. The electric field in the middle is
2000 N/C, downward
A crate is acted upon by a net force of 100 N. An acceleration of 4.0 m/s2results. Theweightof thecrate is
245 N
A man weighs 650 N while on the surface of Earth. If he is transported to the planet Mythos, whichhas the same mass as Earth but a radius that is five times larger than Earth's, his weight would be
26 N
An object weighs 30 newtons on Earth. What is its approximate mass
3 kg
A man standing on a bridge throws a stone horizontally with a speed of 20 m/s. The stone hits the water below 2.5 s later. The bridge is:
30.6 m high
A car is decelerating at the rate of 2 km/s2. If its initial speed is 66 km/s, how long will it take the car to come to a complete stop?
33 s
If the speed of a car is doubled but the brakes apply the same force, the distance required to stop thecar changes by a factor of
4
A 10 kg object dropped from a certain window strikes the ground in 4.0 s. Neglecting air resistance, a 5 kg object dropped from the same window strikes the ground in:
4.0 s
An auto moves 10 meters in the first second of travel, 15 more meters in the next second, and 20 more meters during the third second. The acceleration of the auto is:
5 m/s^2
In order to go from rest to 50 m/s in 10 s, a jet must be able to accelerate at
5 m/s^2
A transformer is to be used to step down voltage from an alternating current source from 220 V to 110 V. If the primary has 120 turns, then the number of turns in the secondary is
60
An iron robot falls from rest at a great height. Neglecting air resistance, what distance has it fallen in the first 3.5 seconds?
60 m
Your mass is 50 kg. Suppose you are standing on a scale in an elevator that starts moving up and increases its speed at the rate of 3 m/s every second. What would be the reading on the scale?
640 N
A body travels at an initial speed of 2.5 m/s. Given a constant acceleration of 0.2 m/s2, what is the speed of the body at time 25 seconds later?
7.5 m/s
If two metal balls each have a charge of -10-6 C and the repulsive force between them is 1 N, how far apart are they? (Coulomb's constant is k=9.0 × 109 N.m2/C2.)
9.5 cm
A quantity that is a measure of how the velocity of a body changes with time is
Acceleration
A 10 µC charge is at the origin. A -15 µC charge is on the x-axis 10 cm to the right of the origin. At what point other than at infinity can a 1 µC charge be placed so that there will be no net electrostatic force on it?
At one point on the x-axis to the left of the positive charge.
A rifle bullet is fired horizontally at the same instant another bullet is allowed to drop from rest at the same height. Which bullet strikes the earth first?
Both strike at the same instant
You have a pair of horizontal parallel plates, with the positive plate above and the negative plate below. How will the lines of constant potential be arranged in this perspective?
Horizontally
An object undergoes uniform circular motion. Which pair of vectors is perpendicular?
Its centripetal acceleration and velocity vectors
All except one of the following require the application of a net force. Which one is the exception
Maintaining an object in motion at a constant velocity.
The starship Enterprise locks onto an alien ship (whose mass is much greater than the Enterprise's mass) with its tractor beam (think of this as a futuristic rope) and starts to pull the alien ship toward it. Neither ship has its propulsion engines running. Which ship has greater acceleration towards the other?
The Enterprise
A battery is causing a large current in a solenoid (helical coil of wire). A bar magnet is held at rest nearby, aligned with the axis of the solenoid, with its south pole closest to the solenoid. The bar magnet is being repelled by the solenoid. Which of the following statements is true of the conventional current in the solenoid?
The current in the solenoid is flowing clockwise as seen from the bar magnet.
You stand on a scale to measure your weight. The reaction to the force the Earth exerts on you is
The force you exert on the Earth
The acceleration of a body cannot be zero at a point where:
The instantaneous velocity is positive but decreasing
A bar magnet is broken in half and the magnetic field around one piece is mapped out. What is wrong with this picture? Picture
There is no south pole.
Which is stronger, the Earth's pull on the Moon, or the Moon's pull on the Earth
They are the same
A 10-kilogram sack of potatoes falls from an airplane. As the velocity of the falling sack increases, so does the air resistance on it. When the air resistance equals 98 N, the acceleration of the sack will be:
Zero
A common experience is to find that a steady pull is required to keep an object moving at constantvelocity, even on a level surface, when friction is present. Analyzing this experience in light of Newton'slaws of motion, the accepted conclusion is that
a frictional force exactly opposes your pull and the first law applies
Three equal negative charges are placed at three of the four corners of a square. The direction of the electric field at the remaining corner of the square is
along the line connecting this corner with the opposite corner, and toward that corner.
The magnetic pole near the Earth's north geographic pole actually has to be
an S pole, because it attracts the N pole of your compass needle.
Two identical coils of wire are placed on a single horizontal wooden broom handle. The coils are separated by a few centimeters. We now run identical currents in the same direction through each coil. The coils experience
an attractive magnetic force.
When you shuffle your feet on a carpet on a dry day, you can accumulate a charge. The fact that you accumulate a charge means that the carpet is
an insulator, because if it weren't, the charge would immediately leave you.
After their rocket engines shut off, astronauts experience weightlessness in the orbiting Space Shuttle
and they are accelerating because they are actually in free fall
The south pole of a bar magnet is moved toward an aluminum ring, along the axis of the ring. As the magnet approaches, the changing magnetic flux induces an electric current in the ring that, when seen from the bar magnet, corresponds to positive charge carriers flowing
clockwise.
Imagine that this classroom contains a constant magnetic field that points from the front to the back. In front of you a negative charge is slowly moving horizontally to your left. As you watch, the magnetic force on the charge
deflects the charge into a counterclockwise vertical circle.
A football is thrown upward at some angle above the horizontal. If we neglect air resistance, then wecan conclude that the acceleration vector of the football is
downward
An object rises at 5.0 m/s under the influence of gravity only. One second later the object is:
falling at 4.8 m/s
Suppose a planet has a mass of 10 times that of the Earth and a radius that is 100 times that of the Earth. The acceleration of gravity on the surface of the planet, expressed in units of the Earth's acceleration of gravity,g, is:
g/ 1000
If the plates of a charged parallel plate capacitor were moved further apart, the potential energy of each of the charges on the capacitor would
increase
A bullet is fired straight down from a hovering helicopter. If we neglect air resistance, then the velocity of the bullet
increases at 9.8 m/s each second
Picture A long straight wire carries a current. A positive charge moves toward the wire in a direction perpendicular to the wire. The direction of the force on the charge will be
parallel to the wire opposite the direction of the current.
The electric field created by a moving negative charge
points toward the charge
A rubber rod is rubbed with fur, so that the fur becomes positive. The rod is then used to charge an electroscope. The charge on the electroscope will be
positive if charged by induction
The south pole of a bar magnet is moved toward a short helical coil of wire (solenoid) along the axis of the coil. The coil has 100 turns and the ends of the coil are connected to form a closed circuit. If the coil is replaced with a single loop of the same type of wire, and the magnet is moved exactly as before, the magnet experiences a force that is
repulsive and 100 times smaller.
When a net horizontal force of 250 N acts on a 50-kg cart that is free to roll on a level surface
the cart accelerates at 5 m/s2
Two equal positive charges are near each other. If we increase the amount of charge on just one of them, then
the electric field at the position of the smaller charge increases
Two cars that have the same mass are moving around a circular track at the same constant speed. Thetrack is perfectly level. If car 1 is at the inner edge of the track and car 2 is at the outer edge, then
the frictional force on car 1 is greater than the frictional force on car 2
Two particles move into a magnetic field. They enter moving at the same speed and direction. The magnitude of the charge on each is known to be the same. One particle curls to the right and the other to the left upon entering the field, the one on the left moving in a larger circle than the one on the right. From this we can say that
the leftward moving particle has more mass and its charge is opposite the other particle.
You toss a ball straight up in the air. At the highest point, the ball's
velocity is zero and the acceleration is downward
Two identical balls are thrown simultaneously from the top of a very tall cliff. Ball A is throwndownward with an initial velocity of 6 m/s, while ball B is thrown straight upward with an initialvelocity of 9.8 m/s. After one second has elapsed, the
velocity of ball B is zero
Two astronauts of equal mass are holding on to each other and moving at a speed of 30 m/s. They push off of each other and one of the astronauts moves in the same direction as the two were initially moving but at 60 m/s. What is the velocity of the second astronaut?
zero
Two current-carrying wires are parallel to one another and separated by 1 cm. If the distance between them is increased to 2 cm the new force will be what factor times the original force?
½
