Physics 101.002††††††† Exam 4 †† Answers††††††††††††††††††††††††††

 

Read each question and its set of answers very carefully.There is only one best answer for each question.Donít be afraid to ask questions of me during the exam.Just raise your hand if you have one.Useful information:g = 32 ft/s2 = 9.8 m/s2.

 


 


1.The product of mass times velocity is most appropriately called

(a) impulse†††††††††††††††††††††††

(b) change in momentum

(c) momentum††††††††††††††††††

(d) change in impulse

 

2.Which of the following is not a vector?

(a) impulse†††††††††††††††††††††††

(b) momentum

(c) mass††††††††††††††††††††††††††††

(d) All of the above

(e) None of the above

 

3.A force times time causes a change in momentum.

(a) True†††††††††††††††††††

(b) False

 

4.Air bags are used in cars to offer you protection during collisions by impeding your motion toward the steering wheel and windshield.Which of the following is true concerning their use?

(a) they apply the large force required to stop you

(b) they reduce the impulse necessary to stop you

(c) they increase the time for you to come to a stop

(d) all of the above

(e) none of the above

 

5."Rolling with a punch" in boxing is done so that

(a) a minimum force from the punch is delivered to the body

(b) the force of the punch is delivered over a shorter period of time causing less pain

(c) the boxer can have more time to plot his next move

(d) the boxer can delay the match

(e) anger is generated faster between the opponents

 

6.A rubber ball and a lump of clay approach a wall with the same momentum.The clay sticks to the wall and the ball bounces off.Which delivers the most punch (impulse) to the wall?

(a) ball††††††††††††††††††††

(b) clay

(c) both deliver the same amount of punch

 

7.Why does a fired gun recoil?

(a) the bullet carries momentum in one direction, the gun must carry an equal amount in the opposite direction

(b) the gun in effect pushes on the bullet, the bullet pushes on the gun in return

(c) the gun applies an impulse to the bullet, the bullet applies an impulse to the gun in return

(d) All of the above

(e) None of the above

 

8.A 10,000‑kg truck traveling north at 36 m/s hits head-on a 1000‑kg car traveling south at 30 m/s.The collision is totally inelastic.What is the speed in m/s of the truck after collision?

(a) 6 ††††

(b) 36 †††††††††††

(c) 30

(d) 17 ††

(e) 35

 

9.A 5‑kg fish swimming at a speed of 1 m/s swallows an absent-minded 1‑kg fish swimming toward it at 4 m/s.The speed (in m/s) of the larger fish after lunch is

(a) 1/2††

(b) 1/5†††††††††††

(c) 1/6

(d) 2/3††

(e) 3/2

 

10. If you push on an immovable wall for an hour, is there any work done on the wall?

(a) Yes††††††††††††††††††††

(b) No

 

11. Which is more powerful?

(a) an engine that does 1000 ftilb of work in 1 second

(b) an engine that does 1000 ftilb in 1.5 seconds

(c) one is just as powerful as the other since they can do the same amount of work

 

12. Doubling one's velocity only doubles one's danger.

(a) True†††††††††††††††††††

(b) False

 

13. An object of mass 6 kg is traveling at a velocity of 30 m/s.How much work was required to obtain this velocity starting from a position of rest?

(a) 180 Joules†††††††††

(b) 36 Joules

(c) 2700 Joules†††††††††††††††††

(d) 5 Joules

(e) 180 N

 

14. Which energy is an energy of position?

(a) kinetic†††††††††††††††††††††††††

(b) heat

(c) potential††††††††††††††††††††††

(d) force x time

(e) watts

 

15. Can a body have momentum without having energy?

(a) Yes††††††††††††††††††††

(b) No

 

16. A car moving initially at 50 kilometers/hour skids with locked brakes to a stop in 10 meters.How far in meters will the car skid to a stop with locked brakes if it is traveling at 200 kilometers/hour?

(a) 20††††††††††††††††††††††

(b) 60

(c) 90††††††††††††††††††††††

(d) 120

(e) 160

 

17. If I have a 100% efficient machine which lifts weights, how much energy must be supplied to it to lift a 2000 lb weight 3 ft?

(a) 6660 ftilb†††††††††

(b) 2000 lb

(c) 6000 hp†††††††††††††††††††††††

(d) 6000 ftilb

 

18. How does a long pole help a tightrope walker to balance himself?

(a) the pole increases his torque

(b) the pole can be rotated rapidly to achieve balance

(c) it doesn't help

(d) the pole increases his rotational inertia

(e) the pole makes the man heavier

 

19. Two kids are sitting on a seesaw as shown.If the kid on the left weighs 75 lb, what must the kid on the right weigh in order to balance the seesaw?

(a) 50 lb

(b) 75 lb

(c) 100 lb

(d) 150 lb

(e) 200 lb

 

20. The center of mass of a pole vaulter can actually pass under the bar as the pole vaulter passes over the bar.

(a) True†††††††††††††††††††

(b) False

 

21. A person with his back to a wall cannot bend down to touch his toes with his hands without bending his knees.Why?

(a) his center of mass would move beyond his area of support and he would fall

(b) angular momentum would not be conserved

(c) he can't develop the appropriate torque

(d) he is in neutral equilibrium

 

22. In class a metronome was used to discuss rotational inertia.When the sliding mass of the metronome was placed as far from the pivot as possible, the period of the pendulum†† ††† ††because the rotational inertia of the pendulum †††††††††† .

(a) decreased, decreased†††

(b) decreased, increased

(c) increased, increased†††††

(d) increased, decreased

 

23. The object below is traveling in a circle at constant speed.What is the direction of the acceleration of the object?

(a) tangent to the circle

(b) between tangent to the circle and perpendicular to the circle

(c) toward the center of the circle

(d) away from the center of the circle

(e) there is no acceleration

 

24. You and a friend are riding on a playground merry‑go‑round.When you try to roll a ball to your friend you notice that it curves.You report that a force caused this curving.What is the name of that force?

(a) centripetal††††††††††

(b) circular

(c) centrifugal††††††††††

(d) normal

(e) coriolis

 

25. In shooting a rubber band one needs to ††††††††††††††††††††††††††† in order to shoot the rubber band farther.

(a) stretch the band as tight as one can

(b) fire it faster

(c) warm the rubber band before shooting

(d) put spin on the rubber band

(e) take longer in the firing of the rubber band

 

26. What is required to change the angular momentum of a system?

(a) a force†††††††††††††††††††††††††

(b) a spin

(c) a jerk†††††††††††††††††††††††††††

(d) a torque

(e) an impulse

 

27. When an ice skater spins with arms outstretched and pulls them inward, the speed at which she spins increases.Does her angular momentum increase?

(a) Yes††††††††††††††††††††

(b) No

 

28. The non-spinning person below is holding a spinning bicycle wheel with its spin "up."The person is standing on a platform that is free to rotate.What happens when the person flips the bicycle wheel over?

(a) nothing

(b) he starts to spin with spin "down"

(c) he starts to spin with spin "up"

(d) the wheel stops spinning

 

 

 

29. If somehow the moon were moved to a distance twice as far away from the earth as it is now, the force that the earth has for the moon would

(a) be twice what it is now

(b) be one half of what it is now

(c) be four times greater than it is now

(d) be one fourth as much as it is now

 

30. The astronauts in the shuttle appear to be weightless.Are they so far from the earth that the gravitational pull of the earth upon them is essentially zero?

(a) Yes

(b) No

 

31. Which moon phase below will result in spring tides on the earth?

(a) first quarter

(b) full

(c) waxing gibbous

(d) third quarter (last quarter)


32. Newton said that the path of a planet curves because a force acts on it.Why does a planet's path curve according to Einstein?

(a) because a force acts on it

(b) because it is spinning

(c) because it is in a geometric warp of space and time