# physics question

I really need help and in-depth explanations on how to do these problems from the online practice test.

1. Use the following working values for the physical constants:

Acceleration due to gravity on the surface of the earth: g = 10 m/s^2

Speed of light in a vacuum: c = 3.0 x 10^8 m/s

Charge of an electron: Qe = 1.6 x 10^-19 coulomb

What is the magnitude of the resultant force, in Newtons, acting on an object that has two forces acting in the same direction having magnitudes of 15 Newtons and 25 Newtons and a third force acting perpendicular to the first two having a magnitude of 30 Newtons?

A. 5

B. 10

C. 40

D. 50

E. 70

2. The universal gravitational law can be written F = Gm1m2/d^2. Which of the following are the units of the constant G?

A. kg^2- m^2/Newton

B. kg^2/(Newton-m^2)

C. 1/Newton

D. Newton-kg^2-m^2

E. Newton-m^2/(kg)^2

3. A vector quantity is BEST described as having

A. a direction only.

B. a magnitude only.

C. units only.

D. a magnitude and a direction.

E. significant figures.

4. Carbon 14 is different than Carbon 12 because it has

A. 2 more protons.

B. 1 more proton and 1 more neutron.

C. 1 more proton and 1 more electron.

D. 2 more electrons.

E. 2 more neutrons.

6. A magnifying glass is constructed when the lens is

A. converging and the object is located at twice the focal length.

B. converging and the object is between the lens and the focal point.

C. diverging and the object is at twice the focal length.

D. diverging and the object is between the lens and the focal point.

8. How many seconds does it take a car traveling 4 m/s to increase its speed to 6 m/s if it has an acceleration of 2 m/s^2?

A. 1

B. 2

C. 3

D. 4

E. 5

9. The acceleration vector is always

A. parallel to the displacement vector.

B. parallel to the velocity vector.

C. parallel to the resultant force vector.

D. perpendicular to the velocity vector.

E. perpendicular to the resultant force vector.

10. A 50-kg girl pulls a 20-kg wagon with a force of 10 Newtons. The wagon accelerates at 2 m/s^2. What is the force, in Newtons, exerted BY the wagon ON the girl?

A. 140

B. 100

C. 40

D. 20

E. 10

11. A small girl applies a horizontal force of 2 Newtons to a 10-Newton box which slides across the floor with a constant speed of 3 m/s. What is the frictional force, in Newtons, by the floor on the box?

A. 2

B. 6

C. 8

D. 10

E. 12

12. A satellite of mass 200 kg completes a circular orbit of the Earth in 120 minutes. A 400 kg satellite is then put into orbit at the same height above the Earth. Which of the following represents the time, in minutes, for the 400 kg satellite to complete a circular orbit?

A. 60

B. 120

C. 180

D. 240

E. 360

13. Atmospheric pressure is very nearly 100 kPa. A sealed container of air at 1 atmospheric pressure has a door 1 m wide and 2 m high. This door is very hard to open during HIGH pressure days. If the atmospheric pressure on the outside of the container is just 1 percent greater than on the inside, then what added force in Newtons is required to open the container door?

A. 100

B. 200

C. 2.000

D. 10,000

E. 20,000

14. An elevator weighing 480 Newtons is supported by a light, vertical cable which exerts a constant force on the elevator, causing the elevator to accelerate upward. Which of the following is the tension, in Newtons, in the cable?

A. Greater than 480

B. Less than 480

C. Equal to 480

D. Data is insufficient to determine the answer

E. 0

16. A ball is thrown horizontally at 20m/s from the top of a building and strikes the level ground 50 m from the building. Approximately how many meters high is the roof of the building?

A. 12.5 m

B. 24.5 m

C. 31 m

D. 50 m

E. 62 m

17. A girl exerted 150 Newtons to lift a barbell 2.0 m in 4.0 s. If she did the same thing in 8.0 s, the work done on the barbell by the girl would be

A. one fourth as great.

B. one half as great.

C. the same.

D. twice as great.

E. four times as great.

18. A block of mass 1 kg, initially at rest, is hit by another block of mass 2 kg, moving initially with a speed of 12 m/s. After the collision, the two blocks move forward as a single composite body. Which of the following is the speed, in m/s, of the composite body?

A. 3

B. 4

C. 6

D. 8

E. 10

19. If friction is neglected, a 2-kg object that has fallen 10 m.

A. has gained potential energy.

B. has lost kinetic energy.

C. will have a constant mechanical energy.

D. has lost 20 Joules of potential energy.

E. has gained 20 Joules of kinetic energy.

20. Which of the following has the largest momentum?

A. A 30,000-kg railroad car traveling at 1 m/s

B. A 200-kg person running at 3 m/s

C. A 1-g bee flying at 5 m/s

D. A 2,000-kg car traveling at 10 m/s

E. A 20-g bullet traveling at 1,000 m/s

21. The amplitude of a body undergoing simple harmonic motion is doubled. Which of the following is also doubled?

A. Maximum speed

B. Frequency

C. Mass

D. Total energy

E. Period

22. If an 80-cm-long spring requires 10 Newtons to stretch 5 cm, how much force, in Newtons, will be needed to stretch the same spring by 8 cm?

A. 8

B. 16

C. 24

D. 50

E. 80

23. An AM radio station broadcasts at a frequency of 600 kHz. If these waves have a speed of 3 x 108 m/s, then what is their wavelength in meters?

A. .0020

B. 500

C. 5000,000

D. 1.80 x 1011

E. 1.80 x 1014

24. In a vacuum, radio waves, microwaves, and x-rays all have the same

A. period.

B. frequency.

C. wavelength.

D. energy.

E. speed.

25. A uniform block of mass 180 g that is 10 x 9 x 3 cm is to be placed in a liquid of density 0.900 g/cm^3. The block will

A. sink in the liquid.

B. just float in the liquid with none of its volume above the surface of the liquid.

C. float in the liquid with more than 1/2 of its volume above the surface of the liquid.

D. float in the liquid with less than 1/3 of its volume above the surface of the liquid.

E. float in the liquid with all of its volume above the surface of the liquid.

26. The water in a swimming pool is 3.0 m deep. During the day, the atmospheric pressure increases by 2.0 x 103 N/m^2. During this same period, the pressure at the bottom of the pool, in N/m^2, will

A. not change.

B. increase by 1.0 x 107.

C. increase by 6.0 x 103.

D. increase by 6.0 x 104.

E. increase by 2.0 x 103.

27. A 600-N force is applied to a safe full of gold which weighs 2000 N, but it does not move. What is the friction force exerted by the floor on the safe?

A. < 600 N

B. 600 N

C. > 600 N but < 2000 N

D. 2000 N

E. > 2000 N

28. If an object is displaced a small distance from an equilibrium position and returns to that position after being released, then which of the following best describes this equilibrium position?

A. Stable equilibrium position

B. Neutral equilibrium position

C. Unstable equilibrium position

D. Position of positive equilibrium

E. Position of negative equilibrium

29. A thin lens produces a virtual image which is smaller than the object. It must be that the

A. object must be inside the focal point of a converging lens.

B. object must be outside the focal point of a converging lens.

C. lens must be a diverging lens.

D. object must be infinitely far from a converging lens.

E. object must be far from the optical axis of a converging lens.

30. An object initially moving with speed 5m/s has acceleration -2m/s^2. Which of the following graphs best represents the object's velocity as a function of time?

31. The Kelvin temperature of an ideal gas is proportional to the average

A. momentum of a molecule in the gas.

B. angular momentum of a molecule in the gas.

C. kinetic energy of a molecule in the gas.

D. net force on a molecule in the gas.

E. moment of inertia of a molecule in the gas.

32. Water boils at 100 C at sea level at atmospheric pressure. At higher pressure, water will boil at (a)

A. higher temperature.

B. lower temperature.

C. 100Ã?° C

D. 0Ã?° C

E. 273 K

33. Which of the following is the cost of lighting a 100-W lamp for 10 hours at $0.10 per kilowatt-hour?

A. $0.01

B. $0.10

C. $0.50

D. $1.00

E. $10.00

34. A negatively charged insulator is brought near to, without touching, the left side of a uncharged, solid metal sphere. Which of the following figures best describes the charge distribution on the sphere with the insulator held in place?

35. A 12-volt battery with an internal resistance of 1 Ohm resistor. Which of the following is the current in amperes that flows in the circuit.

A. 4

B. 3

C. 9

D. 12

E. 48

37. A long straight horizontal wire with a current in it produces a magnetic field that

A. points radially away from the wire.

B. has the same magnitude at all locations.

C. points in the same direction above and below the wire.

D. at any point is perpendicular to the plane containing that point and the wire.

E. points radially toward the wire.

38. As red light goes from the air into water at an angle of incidence of 40Ã?°, which of the following necessarily remains constant?

A. Wavelength of the light

B. Speed of the light

C. Polarization of the light

D. Frequency of the light

E. Direction of travel of the light

39. What is the focal length in cm of a lens that produces an image 30 cm behind it when the object is placed 6 cm in front of it?

A. 7.5

B. 36

C. 5.0

D. 24

E. 18.0

#### Solution Preview

Please find the detailed and complete solution in the attachment.

1. First, 15 N and 25 N have the same direction, so the resultant force of these two forces is:

15 + 25 = 40 N, shown as the red arrow in the above figure.

Now the third force is 30 N, which is perpendicular to 40 N force.

3. Vector has both magnitude and direction.

4. Since they are both carbon, both have 6 protons. The difference comes from the numbers of neutrons.

This little number (12 or 14) is the sum of the proton and neutrons in the atom.

So in carbon 14, it has 14 - 6 = 8 neutrons.

In carbon 12, it has 12 - 6 = 6 neutrons.

They are different isotopes of carbon.

6. First the magnifying glass is a convex lens so it is converging.

Secondly, from the lens equation, we find the magnification of the lens:

Where so and si are the distances from the object to the lens and fro the lens to the image, respectively. And f is the focal length of the lens.

9. The acceleration is the derivative of the velocity function. a= dv/dt . So it is always perpendicular to the velocity vector.

Answer: D

10. By Newton's third law, the force exerted by the girl on the wagon = the force exerted by the wagon on the girl = 10.

Answer: E

13. Pressure = Force / Area

So the force = pressure * area

The area of the door = 1 * 2 = 2 m^2.

The pressure inside the container is 100 kPa

The pressure outside the container is 1% larger = 101 kPa.

To open the door,

F + force exerted on the door by the air inside > = force exerted ...

#### Solution Summary

It provides detailed explanations of a set of physics questions, such as the resultant force, lens, pressure, and boiling temperature.