1: Part Circle the correct answer. Each is worth 5 points.
1. I t t akes no force to accelerate a piece o f s tring that connects t wo m asses.
T RUE
2. I f an object is sliding down a slope, there is at least one direction y ou can pick in which the net force is zero.
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F ALSE
3 . In a modified Atwood machine (block on a ramp connected by string and pulley to a hanging mass), i f you decide that the acceleration o f the block is positive w hen it moves right towards the pulley , what should you pick as the positive direction o f a cceleration for the hanging mass? B .Up
C .Left
D . Right
E. I t d oesn't matter.
4. I f an object is submerged in fluid, where is the pressure the greatest? A. The top o f the object
~ . The bottom o f the object
C. I t's the same o ver the entire object D. It depends on the shape o f the object 5. A sharp knife is safer than a dull one because you don ' t n eed to apply as much force to get the same pressure, making the knife easier to control. F ALSE
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6. I f you push on a shopping cart with 40N o f force, the cart pushes back on your hands with less force , because it weighs a lot less than you _do.
TRUE
7. I f an object is sliding downhill, which force is at least partly in the direction o f " uphill"? " A. Weight B. Normal force
@ Friction
D. All o f the above 8. What is a possible reason for the fact i t's hard to move quickly underwater? A. Water pressure opposes motion more the faster you go. Water viscosity opposes motion more the faster you go. C. Both A and B. D. Neither A nor B.
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9. Dr. Van Domelen weighs 870 N and hops into a pool. At the moment his feet touch the water, how much force pushes up on his feet from the water? A. Less than 870 N About 870 N C. More than 870 N
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10. Once he has settled down and is floating, with how much force does the water push up? A. Less than 870 N
~ b ou t 870 N
More than 870 N
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Part 2: 10 points each for the correct answers.
11. A box is being p ushed a long a flat floor by a force t hat's a ngled 20 down from
the horizontal, and there is friction. D raw the full Free B ody D iagram for the box,
labeling all the forces. (Partial credit for having some forces right.)
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12. Dr. Van D omelen ( m = 88.6 kg) stands on a chair, and each chair leg ends in a round metal disk 1.4 ern in d iameter. A ssuming his weight is distributed evenly across all four legs o f the chair, h ow m uch pressure is there where a disk touches the floor?
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Part 3: Show all work.
13. A metal cube (0.085 kg , 2.5 em on a side) is suspended u nder the surface o f an
unknown fluid by a string that has 0.65 N o f t ension. W hat is the density o f the
fluid? (Hint: it 's less than the density o f the cube, since the cube isn ' t f loating.)
A. (5 points) Define all y our v ariables (i.e. pick a letter to go with the O.Ul.n/ etc.), both the known values and the u nknowns y ou'll need to solve for. B. (5 points) D raw a d iagram o f what's going on , and label
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Part 3: Show all work.
13. A metal cube (0.085 kg, 2.5 em on a side) is suspended under the surface o f an unknown fluid by a string that has 0.65 N o f tension. What is the density o f the fluid ? (Hint: i t's less than the density o f the cube, since the cube i sn't floating.) A. (5 points) Define all your variables (i.e. pick a letter to go with the rJiJl f !l, etc.), both the known values and the unknowns you'll need to solve for. B. (5 points) Draw a diagram o f w hat 's going on, and label it with your variables ( not w ith numbers).
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Part 3: Show all work.
13. A metal cube (0.085 kg, 2.5 cm on a side) is suspended under the surface o f an unknown fluid by a string that has 0.65 N o f tension. W hat is the density o f the fluid? (Hint: it's less than the density o f the cube, since the cube i sn't floating.) A. (5 points) Define all your variables (i .e. pick a letter to go with th li1,iJJJ. , etc.), both the known values and the unknowns y ou'll n eed to solve for. B. (5 points) D raw a d iagram o f w hat's g oing on, and label it with your variables ( not with numbers).
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