Physics 102.001 Fall 2011 Exam 1

���1) What keeps the moon moving, i.e. why doesn’t it slow down and stop?

A) Earth’s gravity keeps it moving. B) The Sun’s gravity keeps it moving. C) It actually is slowing down, and will stop in a few thousand years. D) Nuclear processes operating in the core of the moon. E) It is the natural tendency of every object to keep moving.

2) A ball is moving at 20 m/s. If no forces act on it, then 5 seconds later its speed will be

A) zero. B) more than 20 m/s, but precise answer requires more info. C) less than 20 m/s, but precise answer requires more info. D) 20 m/s. E) None of the above.

3) Today, the idea that everything is made of atoms should be classified as

A) a fact. B) a certainty. C) both of the above. D) a theory. E) a hypothesis.

4) An individual sulfur atom has twice the weight of an individual oxygen atom. What is the weight ratio of sulfur and oxygen in sulfur dioxide?

A) 1 part sulfur to 2 parts oxygen B) 2 parts sulfur to 1 part oxygen C) 1 part sulfur to 4 parts oxygen D) 4 parts sulfur to 1 part oxygen E) 1 part sulfur to 1 part oxygen

5) From a certain point in space you’re observing the moon orbiting counter-clockwise around Earth. Is any net force exerted on the moon?

A) Yes, in the directions of the moon’s instantaneous velocity. B) Yes, towards Earth C) Yes, away from Earth D) No, because no net force is needed to keep an object moving. E) No, because the individual forces acting on the moon all balance out to yield a

net force of zero.

6) We now know that Newtonian physics is not valid for

A) very fast-moving objects. B) stationary objects. C) gases. D) solid objects. E) Nonsense – Newtonian physics has never been found to be invalid.

7) Jill’s weight is 500 N. If Earth gravitationally collapses from its present radius of 6000 km down to a radius of only 600 km, Jill’s weight would then be

A) reduced by a factor of 100. B) unchanged. C) 2000 N. D) 5000 N. E) 50,000 N.

8) A car weighing 3000 N has a forward drive force of 1000 N. Air resistance on the car is 100 N, and rolling resistance is 100 N. The car moves along a straight level road. The net force on this car is

A) 200 N backward. B) 800 N backward. C) 800 N forward. D) 1000 N forward. E) 1200 N forward.

9) A car travels down a level road at constant velocity. One force acting on the car is

A) gravity pushing upward on the car. B) the road pushing upward on the car. C) the road pulling downward on the car. D) the car pushing downward on the road. E) None of the above.

10) A ball is rolling along the floor, toward the east, and slowing down. As it rolls,

A) the net force on it is toward the west. B) its velocity is toward the west. C) Both of the above. D) the net force on it is toward the east. E) the net force on it is zero.

11) The ball’s acceleration in the previous question is

A) zero. B) toward the east. C) toward the west. D) None of the above.

12) The law of inertia says that

A) if there is a force on a body, the body will have a changing acceleration. B) if there is a force on a body, the body will have no acceleration. C) if there is a force on a body, the body will have an unchanging velocity. D) if there is no force on a body, the body will have a changing velocity. E) if there is no force on a body, the body will have no acceleration.

13) You push your 2 kg book along a tabletop, pushing it with 10 N of force. The frictional force on it is 4 N. The book’s acceleration is

A) 0.2 m/s2 B) 5 m/s2 C) 3 m/s2 D) 2 m/s2 E) zero.

14) You are in distant space, where there is (essentially) no gravity, holding two blocks of metal. They look and feel identical when touched, but you’ve been informed that one is made of lightweight aluminum and the other of lead. Can you determine which one is lead without doing any kind of chemical analysis?

A) You can determine this by dropping them – the lead block will fall fastest. B) You can determine this by dropping them – the aluminum block will fall fastest. C) You can determine this by giving each block a push with your finger – the one

that accelerates the most is the lead. D) You can determine this by giving each block a push with your finger – the one

that accelerates the most is the aluminum. E) None of the above methods will work.

15) An apple weighing 3 N hangs, motionless, from a tree branch. Newton’s law of force pairs says that forces always come in pairs. One force acting on the apple is its weight. What is the other force that forms a force pair with the weight?

A) The branch pulling upward on the apple. B) The apple pulling upward on Earth. C) The apple pulling downward on the branch.

D) Earth pulling downward on the apple. 16) The basic physical principle that explains the operation of rocket engines is

A) the law of inertia. B) the law of force pairs. C) Galileo’s principle of falling. D) the atomic hypothesis. E) actually, rockets are unexplainable.

17) We wish to find the net force on a car, in order to apply Newton’s 2nd law, the law of motion. As part of the net force, do we need to include “internal frictional forces” due to internal gears, bearings, etc.?

A) Yes, because these forces dissipate some of the car’s energy. B) Yes, because every internal & external force must be included. C) Yes, because of Newton’s law of force pairs. D) No, because only the drive force needs to be included. E) No, because only external forces need to be included.

18) The number of atoms in the sulfuric acid molecule, H2SO4, is

A) 7 B) 6 C) 4 D) 3

19) Which is heaviest?

A) water molecule B) oxygen atom C) hydrogen atom D) electron E) proton

20) The approximate size of a proton (and also of the lightest atomic nuclei) is one thousandth of a trillionth of a meter. In powers of ten, this is

A) 10-10 m B) 10-14 m C) 10-15 m D) 10-16 m

21) Roughly how many different elements are there?

A) 4 B) 20 C) 100 D) 1000 E) many more than 1000

22) A 2000 kg car moving at 100 km/hr slams into a stationary 3000 kg car, and they stick together. Assuming the wreck is free to move after the collision, its speed will be

A) Not enough information to calculate. B) 40 km/hr C) 50 km/hr D) 100 km/hr E) 25 km/hr

23) In what kind of path would the planets move if no force acted on them?

A) They would continue in their present orbits, since they already have no force acting on them.

B) Larger elliptical orbits C) Parabolas, like a thrown rock D) Straight line with an acceleration of 10 m/s2 E) Straight line with no acceleration

24) On Earth an object is thrown up, and eventually drops back to the ground. At the top of its path (neglecting air resistance) its instantaneous speed and its acceleration are, respectively,

A) zero and zero. B) zero and 10 m/s2, pointing down. C) 10 m/s and zero. D) 10 m/s and 10 m/s2, pointing up. E) None of the above.

25) Between Earth and our moon, would you expect there to be a point where the gravitational forces on an object from Earth and from the moon are equal in magnitude and in the same direction?

A) yes B) no

26) While a rock is falling straight down it has

A) an unchanging speed and an unchanging velocity. B) a changing speed and an unchanging velocity. C) an unchanging speed and a changing velocity. D) A changing speed and a changing velocity.

27) Which of the following describe an object that is moving with an unchanging speed but a changing velocity?

A) A car moving at a steady 80 km/hr along a straight horizontal road. B) A car slowing down while moving in a straight line. C) A car rounding a curve at a steady 80 km/hr. D) A car moving up a straight, constant-slope hill at a steady 80 km/hr, when the

car is about midway up the hill. E) Both answers C and D are correct.

28) A rock is dropped off of a high cliff on another planet, planet X. There is no atmosphere, and thus no air resistance, on planet X. At the end of 1 second, the rock is moving at a speed of 6 m/s. At the end of 2 seconds, it is moving at 12 m/s. How fast will the rock be moving at 4 seconds after being dropped?

A) 18 m/s B) 20 m/s C) 24 m/s D) 36 m/s E) 40 m/s

29) An object falling from rest on Earth (neglecting air resistance) will at the end of the fifth second have an instantaneous speed of approximately

A) 10 m/s B) 50 m/s C) 100 m/s D) 5 m/s E) impossible to determine from the information given

30) If a helium-filled balloon is released on Earth, it rises. That’s because helium gas is less dense than air, i.e. has less mass per volume than air. How would a helium-filled balloon move if it were released a few feet above the surface of the moon?

A) It would rise. B) It would remain suspended at the point of release. C) It would fall at the same rate a rock falls when dropped on the moon.

D) It would fall, but much more slowly than a rock dropped on the moon. 31) Now we’re not neglecting air resistance. A ball is thrown up on Earth. On its way down, the force due to air resistance

A) points in the same direction as the force due to gravity. B) points in the opposite direction as the force due to gravity. C) Neither of the above.

32) A rocket has a mass of 6,000 kg, and its engines are capable of 50,000 N of thrust. What happens to this rocket at liftoff on Earth?

A) It will accelerate upward with an acceleration of about 1.2 m/s2. B) Nothing, not enough thrust for actual liftoff. C) Same as A), but with about 2 m/s2. D) Same as A), but with about 0.5 m/s2.

33) What happens to the same type of rocket as in the previous question upon liftoff from our moon?

A) Nothing, same problem, not enough thrust. B) It will accelerate upward with an acceleration of about 2.5 m/s2. C) Same as B), but with about 4.0 m/s2. D) Same as B), but with about 6.7 m/s2. E) Same as B), but with about 1.5 m/s2.

34) On a frictionless icy surface a stationary person weighing 800 N is thrown a 2 kg object. The object’s speed is 2 m/s, and the person catches the object. What happens next to the person?

A) Nothing. B) He/she recoils in the direction of the object’ s initial velocity with a speed of

approximately 5 cm/s. C) He/she recoils in a different direction from B) and with a speed that can’t be

calculated given the information we have. D) Same as B), but with a speed of approximately 0.1 m/s. E) Same as B), but with a speed of approximately 0.2 m/s.

35) Mary passes Mike from behind while bicycling. As she passes him,

A) the two have the same speeds but different velocities. B) the two have different speeds but the same velocities. C) the two have different speeds and different velocities. D) the two have the same speeds and the same velocities.

36) A car weighing 20,000 N experiences a rolling resistance of 200 N and an air resistance of 300 N. What drive force is needed for this car to achieve an acceleration of 0.5 m/s2?

A) 1000 N B) 2000 N C) 500 N D) 1500 N E) 20,000 N

37) What would happen to the gravitational force between Earth and our moon if the distance from Earth to the moon would triple?

A) It would also triple. B) It would decrease by a factor of 3. C) It would decrease by a factor of 9. D) Nothing, it would stay the same. E) It would decrease by a factor of 4.

38) Estimate the gravitational force (in N) that you exert on another person standing about 1 m away. Is it closer to

A) 1 N B) 1000 N C) 10-3 N D) 10-6 N E) 10-11 N

39) You’re making a right-hand turn in your car. Why do you tend to lean into the left-hand door?

A) You tend to continue to go straight while the car moves towards the right. B) Newton’s Third Law. C) Friction pushes you to the left. D) Your inertia pushes you to the left. E) The door has it in for you.

40) Suppose you throw an apple horizontally. Neglecting air resistance, just after you release the apple from your hand, the net force on the apple is

A) zero. B) directed horizontally backward. C) directed horizontally forward. D) directed upward.

E) directed downward. Answers:

1. E 2. D 3. D 4. E 5. B 6. A 7. E 8. C 9. B 10. A 11. C 12. E 13. C 14. D 15. B 16. B 17. E 18. A 19. A 20. C 21. C 22. B 23. E 24. B 25. B 26. D 27. C 28. C 29. B 30. C 31. B 32. B 33. D 34. B 35. C 36. D 37. C 38. D 39. A 40. E