Physics test #3

4. Big Bubba has a mass of 100 kg on the earth. What is Big Bubba's mass on the moon where the force of gravity is approximately 1/6-th that of Earth's? ________ Explain or show your work.

100kg

3. Which of the following statements are true of the quantity weight? List all that apply. The weight of an object is dependent upon the value of the acceleration of gravity. Weight refers to a force experienced by an object. The weight of an object would be less on the Moon than on the Earth. A person could reduce their weight significantly by taking an airplane ride to the top of Mount Everest. Two objects of the same mass can weigh differently. To gain weight, one must put on more mass. The weight of an object can be measured in kilograms. The weight of an object is equal to the force of gravity acting upon the object. When a chemistry student places a beaker on a balance and determines it to be 84.3 grams, they have weighed the beaker.

ABCH and maybe EF

7. Consider Newton's second law of motion to determine which of the following statements are true? List all that apply. If an object is accelerating to the right, the net force on the object must be directed towards the right. If an object is moving to the right and slowing down, then the net force on the object is directed towards the left. Accelerating objects are either slowing down or speeding up. The acceleration of an object is directly dependent upon its mass and inversely dependent upon its net force. An object has an acceleration of 8 m/s/s. If the net force acting upon the object is increased by a factor of 2, then the new acceleration would be 10 m/s/s. An object has an acceleration of 8 m/s/s. If the net force acting upon the object is increased by a factor of 3, then the new acceleration would be 11 m/s/s. An object has an acceleration of 8 m/s/s. If the mass of the object is increased by a factor of 2, then the new acceleration would be 16 m/s/s. An object has an acceleration of 8 m/s/s. If the mass of the object is increased by a factor of 4, then the new acceleration would be 2 m/s/s. An object has an acceleration of 8 m/s/s. If the net force acting upon the object is increased by a factor of 2 and the mass of the object is decreased by a factor of 2, then the two factors would offset each other and the acceleration would still be 8 m/s/s. An object has an acceleration of 8 m/s/s. If the net force acting upon the object is increased by a factor of 2 and the mass of the object is increased by a factor of 4, then the new acceleration would be 4 m/s/s. An object has an acceleration of 8 m/s/s. If the net force acting upon the object is decreased by a factor of 2 and the mass of the object is increased by a factor of 4, then the new acceleration would be 1 m/s/s. An object has an acceleration of 8 m/s/s. If the net force acting upon the object is increased by a factor of 4 and the mass of the object is increased by a factor of 2, then the new acceleration would be 16 m/s/s. A 2-kg object accelerates from rest to a final velocity of 6 m/s in 3 seconds. The magnitude of the net force acting upon the object is 12 N. A 10-kg object slows down from 24 m/s to a final velocity of 9 m/s in 3 seconds. The magnitude of the net force acting upon the object is 80 N.

ABHJKL

3. Which of the following are never true of an object that is at equilibrium? Include all that apply. The object is accelerating. The object is at rest. The object is moving in a circle at constant speed. All the forces acting upon the object are equal. The object is in free-fall. The object is falling and has reached its terminal velocity. There is a net force acting upon the object. The object is moving and moving with a constant velocity.

ACEG

6. Which of the following statements are true of the concept of force? List all that apply. A force is a push or pull exerted upon an object which results from the interaction of that object with its environment. Bubba approaches Billie and gives him a swift shove. Timid little Billie keeps his hands in his pocket during this interaction. Subsequently, while Bubba places a force upon Billie, Billie does not place a force upon Bubba. A quarterback throws a football down field. Once thrown, the force from the quarterback persists upon the ball to cause it to continue on its upward trajectory towards its peak. A sled slides down the hill and reaches the bottom where it gradually slows to a stop. Once on the level ground, the force of the hill persists upon the sled to allow it to continue its forward motion. Forces always cause objects to move. An object can experience two or more forces and not accelerate. A contact force results from the physical contact between two objects. A field force results from the action of two objects which are positioned some distance away. Spring and tension forces are examples of field forces. A force is a vector quantity; there is always a direction associated with it. Force can be measured in kilograms or Newtons depending upon the system of measurement (metric or otherwise).

AFGJ and maybe H

5. Consider Newton's first law of motion to determine which of the following statements are true? List all that apply. Newton's first law of motion is applicable to both moving and nonmoving objects. If a football is moving upwards and rightwards towards the peak of its trajectory, then there are both rightwards and upwards forces acting upon it. It would take an unbalanced force to keep an object in motion. If an object is at rest, then there are no forces acting upon the object. It would take an unbalanced force to keep an object in motion at a constant velocity. It is the natural tendency of all objects to eventually come to a rest position. A pendulum bob is set into its usual back-and-forth periodic motion. After some time (perhaps 10 minutes), the pendulum bob comes to a rest position. This is best explained by the idea of inertia - all objects eventually resist motion. If a 3-kg rock is thrown at a speed of 2 m/s in a gravity-free environment (presuming one could be found), then an unbalanced force of 6 N would be required to keep the rock moving at a constant speed. It would take an unbalanced force to cause an object to accelerate from rest

AI

7. How much net force is required to keep a 5-kg object moving rightward with a constant velocity of 2 m/s? ________ Explain or show your work.

Answer: 0 N If the velocity is constant, then the acceleration is 0 m/s/s and the net force is zero. A net force is only required in order to accelerate an object. Yes, this means that an object can be moving to the right and NOT have a rightward's net force. (If you're getting stuck on this question and ones like them, it might be time to read the page titled "The Big Misconceptsion"; use the link below.)

5. Little Billie weight 360 N on Earth. What is Little Billie's mass on the moon where the force of gravity is approximately 1/6-th that of Earth's? ________ Explain or show your work.

Answer: 37 kg (approx.) The acceleration of gravity on the moon is 1/6-th the value of earth's; this explains why the force of gravity is 1/6-th that of earth's. The force of gravity (Fgrav) on the moon is calculated using the equation Fgrav = m•g where g =1.6 m/s/s (on the moon). If Little Billie's weight on the moon is 1/6-th of 360 N, then Little Billie weighs 60 N on the moon. Inserting 60 N into the equation with 1.6 m/s/s as the value of g, Little Billie's mass can be calculated to be approximately 37 N. (Alternatively, simply find Billie's mass on earth from his weight of 360 N and then conclude that this mass value is not going to change when he goes to the moon.)

10. Three pictures of equal weight (20 N) are hung by wires in three different orientations. In which orientation are the wires least likely to break? _______ Explain why.

Answer: 60-degree angle to the horizontal The tension in the wire will have the greatest impact upon its tendency to break. As the wire becomes most vertically oriented, the horizontal component of the tension force is reduced and the tension becomes less. The moral of the story -- to support the weight of a picture, one only needs to pull upwards, not leftwards and rightwards. Of course, the best arrangement would be two wires pulling completely vertically.

For an object resting upon a non-accelerating surface, the normal force is equal to the force of gravity.

Answer: FALSE Could be on an incline

9. An object rests upon an inclined plane. If the angle of incline is increased, then the normal force would _______. a. increase b. decrease c. remain the same

B

2. Which of the following statements are true of the quantity mass? List all that apply. The mass of an object is dependent upon the value of the acceleration of gravity. The standard metric unit of mass is the kilogram. Mass depends on how much stuff is present in an object. The mass of an object is variable and dependent upon its location. An object would have more mass on Mount Everest than the same object in the middle of Lake Michigan. People in Weight Watcher's are really concerned about their mass (they're mass watchers). The mass of an object can be measured in pounds. If all other variables are equal, then an object with a greater mass would have a more difficult time accelerating. If all other variables are equal, then it would require less exerted force to stop a less massive object than to stop a more massive object. The mass of an object is mathematically related to the weight of the object.

BCFHIJ

Each one of Newton's Laws can play a role in any one particular situation. However, one of the laws is often most obviously dominant in governing the motion of a situation. Pick which of Newton's most governs the situations described below. a. First Law (inertia) b. Second Law (F = m•a) c. Third Law (action-reaction) 16. A helicopter must have two sets of blades in order to fly with stability. 17. If you were in an elevator and the cable broke, jumping up just before the elevator hit the ground would not save you. Sorry. 18. You usually jerk a paper towel from a roll in order to tear it instead of pulling it smoothly. 19. A student desk changes the amount of force it puts on other objects throughout a school day. 20. Heavy objects are not easier to move around in a horizontal fashion on the Moon than on the Earth. 21. The stronger, heavier team in a tug-of-war does not create a larger tension in the rope than the weaker, lighter team.

C A A C A C

13. According to Newton's third law, every force is accompanied by an equal and opposite reaction force. The reason that these forces do not cancel each other is ____. a. the action force acts for a longer time period b. the two forces are not always in the same direction c. one of the two forces is greater than the other d. the two forces act upon different objects; only forces on the same object can balance each other. e. ... nonsense! They do cancel each other. Objects accelerate because of the presence of a third force.

D

11. A 50-N force is applied at an angle of 30 degrees north of east. This would be the same as applying two forces at 43 N, east and 7 N, north 35 N, east and 15 N, north 25 N, east and 25 N, north 43 N, east and 25 N, north

D find components

1. Which of the following statements are true of inertia? List all that apply. Inertia is a force. Inertia is a force which keeps stationary objects at rest and moving objects in motion at constant velocity. Inertia is a force which brings all objects to a rest position. All objects have inertia. A more massive object has more inertia than a less massive object. Fast-moving objects have more inertia than slow-moving objects. An object would not have any inertia in a gravity-free environment (if there is such a place). Inertia is the tendency of all objects to resist motion and ultimately stop. In a gravity-free environment (should there be one), a person with a lot of inertia would have the same ability to make a turn as a person with a small amount of inertia.

DE

2. Which of the following are always true of an object that is at equilibrium? Include all that apply. All the forces acting upon the object are equal. The object is at rest. The object is moving and moving with a constant velocity. The object has an acceleration of zero. There is no change in the object's velocity. The sum of all the forces is 0 N. All the forces acting upon an object are balanced.

DEFG

14. As you sit in your chair and study your physics (presuming that you do), the force of gravity acts downward upon your body. The reaction force to the force of the Earth pulling you downward is ___. a. the force of the chair pushing you upward b. the force of the floor pushing your chair upward c. the force of the Earth pushing you upward d. the force of air molecules pushing you upwards e. the force of your body pulling the Earth upwards f. ... nonsense! Gravity is a field force and there is no such reaction force.

E

An object which is moving rightward has a rightward force acting upon it.

FALSE

12. Which one(s) of the following force diagrams depict an object moving to the right with constant speed? Write all possible answers (if any) in the blank: ________________ Explain your answer(s) to this question.

a c net force zero balanced forces not accelerating

force=

acceleration=change in motion

Which of the following have a direct effect upon the amount of air resistance experienced by an object speed air density cross sectional area

all of them

once terminal vel is reached the force of air resistance is ______________ the force of gravity

equal to

15. A golf pro places a ball at rest on the tee, lines up his shot, draws back his club, and lets one rip. During the contact of the golf club with the golf ball, the force of the club on the ball is ____ the force of the ball on the club and the acceleration of the club is ____ than the acceleration of the ball. a. greater than, greater than b. greater than, equal to c. greater than, less than d. less than, less than e. less than, equal to f. less than, greater than g. equal to, equal to h. equal to, greater than i. equal to, less than

i

as an object moves faster the amount of air resistance

increases

Does the coefficient of friction change if the weight of the object changes? Explain.

no

does the coefficient of kinetic friction depend on speed

no

do action reaction pairs result in equlibrium

no since they act on seperat objects

4. Which of the following statements are true of an object that experiences balanced forces (or unbalanced forces)? List all that apply. If a person is moving to the right, then the forces acting upon it are NOT balanced. A balance of forces is demonstrated by an object which is slowing to a stop. It would take an unbalanced force to keep an object in motion. If an object is moving with a constant speed in a circle, then the forces acting upon the object are balanced. If an object is accelerating at a constant rate of acceleration, then the forces acting upon the object are balanced. It is NOT possible for just three forces to be acting upon an object and they still balance each other. A free-falling object experiences a balance of forces. Balanced forces cause stationary objects to remain at rest and moving objects to come to rest. Unbalanced forces cause objects to move.

none except maybe I

A bug splatters against the windshield of a moving car. Compared to the force of the car on the bug, the force of the bug on the car is...

the same

does the force of kinetic friction depend on the weight of an object

yes