Regents Physics
In a 4.0-kilometer race, a runner completes the first kilometer in 5.9 minutes, the second kilometer in 6.2 minutes, the third kilometer in 6.3 minutes, and the final kilometer in 6.0 minutes. What was the average speed of the runner?
.16 km/min. Average speed is total distance over total time.
A 5-newton force causes a spring to stretch 0.2 meter. What is the potential energy stored in the stretched spring?
.2 J, use PEs = .5kx^2
In a flashlight, a battery provides a total of 3.0 volts to a bulb. If the flashlight bulb has an operating resistance of 5.0 ohms, the current through the bulb is
.6 A Use Ohm's law V= IR
A 10.-newton force is required to hold a stretched spring 0.20 meter from its rest position. What is the potential energy stored in the stretched spring?
1 J. Using F= kx solve for k, then plug into PEs = .5kx^2
If the average force on the 1-kilogram cart is 1 newton, what is the average force on the connected 2-kilogram cart?
1 N. Forces have equal and opposite reactions
A 40.-kilogram mass is moving across a horizontal surface at 5.0 meters per second. What is the magnitude of the net force required to bring the mass to a stop in 8.0 seconds?
1 N. Using conservation of momentum set mv = Ft and plug in the knowns to solve for F.
A 400-newton girl standing on a dock exerts a force of 100 newtons on a 10 000-newton sailboat as she pushes it away from the dock. How much force does the sailboat exert on the girl?
100 N. Forces have equal and opposite reactions.
A 330.-ohm resistor is connected to a 5.00-volt battery. The current through the resistor is
15.2 mA. Use Ohm's law V=IR
A car travels 90. meters due north in 15 seconds. Then the car turns around and travels 40. meters due south in 5.0 seconds. What is the magnitude of the average velocity of the car during this 20.-second interval?
2.5 m/s. Average velocity can be found by dividing total displacement over total time.
A spring scale reads 20. newtons as it pulls a 5.0-kilogram mass across a table. What is the magnitude of the force exerted by the mass on the spring scale?
20N. Every force has an equal and opposite reaction.
The resistance of a 60.-watt lightbulb operated at 120 volts is approximately
240 ohms. Use Ohm's law V= IR
An object weighing 15 newtons is lifted from the ground to a height of 0.22 meter. What is the increase in the object's gravitational potential equal to?
32 J. Use PE = mgh
A 2.0-kilogram body is initially traveling at a velocity of 40. meters per second east. If a constant force of 10. newtons due east is applied to the body for 5.0 seconds, what is the body's final speed?
65 m/s. Using mv=Ft determine the change in velocity and add it to the initial because both are directed east.
A 1.5-kilogram lab cart is accelerated uniformly from rest to a speed of 2.0 meters per second in 0.50 second. What is the magnitude of the force producing this acceleration?
6N using conservation of momentum set m(change in v) = Ft
Two identical resistors connected in parallel have an equivalent resistance of 40. ohms. What is the resistance of each resistor?
80 ohms. Resistors in parallel can be determined by 1/req = 1/r1 + 1/r2
A golf ball is hit at an angle of 45° above the horizontal. What is the acceleration of the golf ball at the highest point in its trajectory?
9.8 m/s^2 downward. The only force acting on the object is the force of gravity downwards.
What does the slope of the graph with gravitational force as the y-axis and mass as the x- axis represent?
Acceleration due to gravity. Fg = mg
One car travels 40. meters due east in 5.0 seconds, and a second car travels 64 meters due west in 8.0 seconds. During their periods of travel, what quantity was equal for both cars?
Average Speed. Car A's average speed was 8m/s and so was Car B's. This can be determined by dividing the total distance by the total time.
A 55.0-kilogram diver falls freely from a diving platform that is 3.00 meters above the surface of the water in a pool. When she is 1.00 meter above the water, whatis her kinetic energy with respect to the water's surface when her PE = 540J?
KE = 1080J subtract the PE from the total energy found by using mgh.
When a force moves an object over a rough, horizontal surface at a constant velocity, the work done against friction produces an increase in the object's
Internal energy, or heat
If the direction of a moving car changes and its speed remains constant, which quantity must remain the same?
Kinetic energy, which is scalar, ie it doesn't take direction into account
The force required to start an object sliding across a uniform horizontal surface is larger than the force required to keep the object sliding at a constant velocity. The magnitudes of the required forces are different in these situations because the force of kinetic friction is what relative to the force of static friction?
Kinetic friction is less than static friction because the applied force must be greater in order for the object to be moving
A child is riding on a merry-go-round. As the speed of the merry-go-round is doubled, how is the magnitude of the centripetal force acting on the child changed?
Quadrupled. Fc = (mv^2)/r
If the potential difference applied to a fixed resistance is doubled, the power dissipated by that resistance
Quadruples, P = V^2/R
A 0.2-kilogram red ball is thrown horizontally at a speed of 4 meters per second from a height of 3 meters. A 0.4-kilogram green ball is thrown horizontally from the same height at a speed of 8 meters per second. How does the time it takes the green ball to reach the ground compare to the the time it takes the red ball to reach the ground?
The same time, because horizontal speed has no impact on vertical velcotiy.
A man is pushing a baby stroller. Compared to the magnitude of the force exerted on the stroller by the man, the magnitude of the force exerted on the man by the stroller is
The same, forces have equal and opposite reactions
A 2.0 × 10^3-kilogram car travels at a constant speed of 12 meters per second around a circular curve of radius 30. meters.As the car goes around the curve, what direction is Fc directed in?
Toward the center of the curve. Fc always points towards the center of the curve/circle.
What unit is equivalent to a newton per kilogram?
m/s^2, N = kgm/s^2
What is the energy equivalent of 5.0 × 10^3 kilogram?
4.5 x 10^14 J. Use E= mc^2
A 2.0 × 10^3-kilogram car travels at a constant speed of 12 meters per second around a circular curve of radius 30. meters.What is the magnitude of the centripetal acceleration of the car as it goes around the curve?
4.8 m/s^2. Use a = v^2/r
How far will a brick starting from rest fall freely in 3.0 seconds?
44 m. Use d = vit+.5at^2.
A vector makes an angle, with the horizontal. The horizontal and vertical components of the vector will be equal in magnitude if angle is how many degrees?
45, components are found by multiplying the initial quantity by the sin and cos of the angle. sin 45 = cos 45
A 0.25-kilogram baseball is thrown upward with a speed of 30. meters per second. What is the max height reached by the ball?
46 m. Use .5mv^2 = mgh
A net force of 10. newtons accelerates an object at 5.0 meters per second^2. What net force would be required to accelerate the same object at 1.0 meter per second^2?
5 N. Solve for the object's mass using the first force and F=MA then using the mass and the second acceleration find the force.
A 50.-kilogram student threw a 0.40-kilogram ball with a speed of 20. meters per second. What was the magnitude of the impulse that the student exerted on the ball?
8 Ns. Using the numbers for just the ball plug into p=mv
A 60.0-kilogram runner has 1920 joules of kinetic energy. At what speed is she running?
8 m/s. Backsolve using KE = .5mv^2
A golf ball is hit with an initial velocity of 15 meters per second at an angle of 35 degrees above the horizontal. What is the vertical component of the golf ball's initial velocity?
8.6 m/s. Find the vertical component by multiplying the initial quantity by the sine of the angle.
Velocity is to speed as displacement is to what?
Distance, speed is the scalar quantity while velocity is vector and distance is the corresponding scalar to displacement.
The magnitude of the electrostatic force between two point charges is F. If the distance between the charges is doubled, the electrostatic force between the charges will become what?
F/4 Fe= (kqq)/r^2
Two weightlifters, one 1.5 meters tall and one 2.0 meters tall, raise identical 50.-kilogram masses above their heads. Compared to the work done by the weightlifter who is 1.5 meters tall, the work done by the weightlifter who is 2.0 meters tall is
Greater, W=Fd so the greater the distance the more work
An outfielder throws a baseball to the first baseman at a speed of 19.6 meters per second and an angle of 30.° above the horizontal. What is vx and vy?
vx = 16.9 m/s vy = 9.8 m/s Use the equations vx = vcos(theta) and vy = vsin(theta).
When a mass is placed on a spring with a spring constant of 15 newtons per meter, the spring is compressed 0.25 meter. How much elastic potential energy is stored in the spring?
.47 J. Use F= kx to solve for k then plug into PEs = .5kx^2
A basketball player jumped straight up to grab a rebound. If she was in the air for 0.80 second, how high did she jump?
.78 m. Use d=vit +.5at^2
A ball thrown vertically upward reaches a maximum height of 30. meters above the surface of Earth. What is the speed of the ball at its max height?
0 m/s. At the max height the ball is switching directions and not moving.
If a box is at rest, the net force acting on it is equal to what?
0, the box must be in equilibrium so all forces must cancel out.
A child kicks a ball with an initial velocity of 8.5 meters per second at an angle of 35º with the horizontal, as shown. The ball has an initial vertical velocity of 4.9 meters per second and a total time of flight of 1.0 second. What is the maximum height of the ball?
1.2 m. Since an object's max height occurs halfway through it's path use t = .5s. Then using d=vit+.5at^2 solve for d.
A 95-kilogram student climbs 4.0 meters up a rope in 3.0 seconds. What is the power output of the student?
1.2 x 10^3 W. Use mgh/t
A 1,200-kilogram car traveling at 10. meters per second hits a tree and is brought to rest in 0.10 second. What is the magnitude of the average force acting on the car to bring it to rest?
1.2 x 10^5 N. Using conservation of energy set mv = Ft and solve for F.
A skater increases her speed uniformly from 2.0 meters per second to 7.0 meters per second over a distance of 12 meters. What is he magnitude of her acceleration as she travels this 12 meters?
1.9 m/s^2. This can be determined by using the formula vf^2=vi^2 + 2ad, solving for a while plugging in the known variables.
A potential drop of 50. volts is measured across a 250-ohm resistor. What is the power developed in the resistor?
10 W. P= V^2/R
Ball A of mass 5.0 kilograms moving at 20. meters per second collides with ball B of unknown mass moving at 10. meters per second in the same direction. After the collision, ball A moves at 10. meters per second and ball B at 15 meters per second, both still in the same direction. What is the mass of ball B?
10 kg. Using convervation of momentum set mavai + mbvbi = mavaf + mbvbf and solve for mb
When a 12-newton horizontal force is applied to a box on a horizontal tabletop, the box remains at rest. The force of static friction acting on the box can be approximated to what?
12 N. The box is not moving so it must be in equilibrium.
A student does 60. joules of work pushing a 3.0-kilogram box up the full length of a ramp that is 5.0 meters long. What is the magnitude of the force applied to the box to do this work?
12 N. W = FD, plug in the knowns and solve for F.
The current through a lightbulb is 2.0 amperes. How many coulombs of electric charge pass through the lightbulb in one minute?
120 C. Use I = Q/T
A 6.8-kilogram block is sliding down a horizontal, frictionless surface at a constant speed of 6.0 meters per second. What is the kinetic energy of the block?
120 J. Use KE = .5mv^2
A 100.-ohm resistor and an unknown resistor are connected in series to a 10.0-volt battery. If the potential drop across the 100.-ohm resistor is 4.00 volts, the resistance of the unknown resistor is
150 ohms. Use the known resistor and Ohm's law to solve for the current (which is the same in series), .04 A, then solve for the total resistance 250 ohms and subtract the known resistance from the total resistance.
A 45.0-kilogram boy is riding a 15.0-kilogram bicycle with a speed of 8.00 meters per second. What is the combined kinetic energy of the boy and the bicycle?
1920 J Use KE = .5mv^2 and combine the weight of the boy and the bicycle
What is the speed of a 1.0 × 10^3kilogram car that has a momentum of 2.0 × 10^4 kilogram•meters per second east?
1x 10^4 m/s. Using p = mv solve for v.
If 10. coulombs of charge are transferred through an electric circuit in 5.0 seconds, what is the current in the circuit?
2 A. I = Q/T
A 60.-kilogram rollerskater exerts a 10.-newton force on a 30.-kilogram rollerskater for 0.20 second. What is the magnitude of the impulse applied to the 30.-kilogram rollerskater?
2 Ns. Use p = Ft
In an electric field, 0.90 joule of work is required to bring 0.45 coulomb of charge from point A to point B. What is the electric potential difference between points A and B?
2 V Use W = V/Q
A 2.0-kilogram laboratory cart is sliding across a horizontal frictionless surface at a constant velocity of 4.0 meters per second east. What will be the cart's velocity after a 6.0-newton westward force acts on it for 2.0 seconds?
2 m/s west. Use Ft = mv to solve for the change in velocity then subtract that from the initial velocity. Since it is still negative it is going west.
A car initially traveling at a speed of 16 meters per second accelerates uniformly to a speed of 20. meters per second over a distance of 36 meters. What is the magnitude of the car's acceleration?
2 m/s^2. Use vf^2 = vi^2 + 2ad
A ball dropped from rest falls freely until it hits the ground with a speed of 20 meters per second. The time during which the ball is in free fall is approximately
2 s. Use vf = vi + at
The speed of a wagon increases from 2.5 meters per second to 9.0 meters per second in 3.0 seconds as it accelerates uniformly down a hill. What is the magnitude of the acceleration of the wagon during this 3.0-second interval?
2.2 m/s^2. Use vf = vi + at
What is the gravitational potential energy with respect to the surface of the water of a 75.0- kilogram diver located 3.00 meters above the water?
2.21 * 10^3 J. Use PE = mgh
A 1.0-kilogram ball is dropped from the roof of a building 40. meters tall. What is the approximate time of fall?
2.9 s. Use d = vit +.5at^2
A girl leaves a history classroom and walks 10. meters north to a drinking fountain. Then she turns and walks 30. meters south to an art classroom. What is the girl's total displacement from the history classroom to the art classroom?
20 m South. Displacement is the location of the final position's magnitude and direction from the starting point, not the total amount travelled.
A 40.-kilogram student runs up a staircase to a floor that is 5.0 meters higher than her starting point in 7.0 seconds. What is the student's power output?
280 W. Use mgh/t
At the circus, a 100.-kilogram clown is fired at 15 meters per second from a 500.-kilogram cannon. What is the recoil speed of the cannon?
3 m/s. Use mclownvclown = mcanonvcanon due to conservation of momentum
If 4.8 × 10^17 joule of work is required to move an electron between two points in an electric field, what is the electric potential difference between these points?
3 x 10^2 V. W = V/Q
When a 1.53-kilogram mass is placed on a spring with a spring constant of 30.0 newtons per meter, the spring is compressed 0.500 meter. How much energy is stored in the spring?
3.375 J. Use F=kx to find k then plug into PEs = .5kx^2
An electric iron operating at 120 volts draws 10. amperes of current. How much heat energy is delivered by the iron in 30. seconds?
3.6 x 10^4 J. W = IV/T
A motor used 120. watts of power to raise a 15-newton object in 5.0 seconds. Through what vertical distance was the object raised?
360 m. Backsolve using P = mgh/t
A 5.0-newton force could have perpendicular components of what?
3N and 4N. Solve using the pythagorean theorm
The spring in a scale in the produce department of a supermarket stretches 0.025 meter when a watermelon weighing 1.0 × 102 newtons is placed on the scale. What is its spring constant?
4 x 10 ^3 N/m. Use F=kx
What is the average power developed by a motor as it lifts a 400.-kilogram mass at constant speed through a vertical distance of 10.0 meters in 8.0 seconds?
4,900 W. P = W/T or P = mgh/T
A 0.50-kilogram ball is thrown vertically upward with an initial kinetic energy of 25 joules. Approximately how high will the ball rise?
5.1 m. Set the initial KE equal to mgh and solve for h.
A vertical spring 0.100 meter long is elongated to a length of 0.119 meter when a 1.00-kilogram mass is attached to the bottom of the spring. What is the spring constant of the spring?
520 N/m. Use F=kx
In a simple electric circuit, a 110-volt electric heater draws 2.0 amperes of current. What is the resistance of the heater?
55 ohms. Using V = IR plug in knowns and solve for R.
A 60-kilogram skydiver is falling at a constant speed near the surface of Earth. The magnitude of the force of air friction acting on the skydiver is what?
600 N. Friction is equal to the opposing force if the object is moving at a constant velocity.
A projectile is fired with an initial velocity of 120. meters per second at an angle above the horizontal. If the projectile's initial horizontal speed is 55 meters per second, then angle measures approximately
63 degrees. Divide the horizontal speed by the initial velocity and take the inverse cosine.
A child kicks a ball with an initial velocity of 8.5 meters per second at an angle of 35º with the horizontal, as shown. The ball has an initial vertical velocity of 4.9 meters per second and a total time of flight of 1.0 second. What is the horizontal component of the ball's velocity?
7 m/s. This can be found by multiplying the initial velocity by the cosine of the angle the ball was kicked at.
The spring of a toy car is wound by pushing the car backward with an average force of 15 newtons through a distance of 0.50 meter. How much elastic potential energy is stored in the car's spring during this process?
7.5 J. Using F = kx solve for the spring constant of the spring. Then use PEs = .5kx^2
A 1-kilogram rock is dropped from a cliff 90 meters high. What is the kinetic energy of the rock after it falls 20 meters?
700 J. Since energy is conserved set the total potential energy equal to the sum of the potential and kinetic energies and solve for the kinetic energy.
A ball is thrown horizontally at a speed of 24 meters per second from the top of a cliff. If the ball hits the ground 4.0 seconds later, approximately how high is the cliff?
78 m. Use d = vit + .5at^2
As a ball falls freely (without friction) toward the ground, its total mechanical energy changes how?
It doesn't as energy cannot be created or destroyed
What happens to the kinetic energy of an object as it falls?
It increases as there is a smaller height that the object is at and its speed increases.
As the potential difference across a given resistor is increased, what happens to the power expended in moving charge through the resistor?
It increases because P = V^2/R
If the speed of a car is doubled, what will happen to its kinetic energy?
It is quadrupled because KE = .5mv^2 and 2^2 = 4.
What happens to an object's acceleration while it is traveling along a parabolic path?
It remains the same as the only force acting on the object, gravity, remains constant.
A ball is thrown at an angle of 38° to the horizontal. What happens to the magnitude of the ball's vertical acceleration during the total time interval that the ball is in the air?
It remains the same. The force acting on the ball, the force of gravity, is constant therefore leaving a constant acceleration.
What is a watt in SI units?
J/S. P = W/T
A box is pushed toward the right across a classroom floor. What direction is the force of friction acting on the box?
Left, the force of friction is always directed in the direction that opposes motion.
Compared to the force needed to start sliding a crate across a rough level floor, the force needed to keep it sliding once it is moving is
Less, the static force of friction is greater than the kinetic force of friction
If the sum of all the forces acting on a moving object is zero, what is the object doing?
Moving with a constant velocity. There is no force causing a change in the object's movement.
The amount of work done against friction to slide a box in a straight line across a uniform, horizontal floor depends most on what quantity?
The distance the box is moved or the force applied to it. This is because W = Fd.
What object would have the most inertia?
The most massive object, because inertia is a measurement of how resistant an object is to forces.
A ball of mass M at the end of a string is swung in a horizontal circular path of radius R at constant speed V. Which combination of changes would require the greatest increase in the centripetal force acting on the ball?
doubling V and halving R. The formula for centripetal force is Fc = (mV^2) / R. This change would create an Fc 8 times greater.
The work done in moving a block across a rough surface and the heat energy gained by the block can both be measured in
joules, measures change in energy