Phy 110- Ch. 02 HW

Part D: Imagine holding a basketball in both hands, throwing it straight up as high as you can, and then catching it when it falls. At which points in time does a zero net force act on the ball? Ignore air resistance. Check all that apply. -just after the ball first leaves your hands -when you hold the ball still in your hands after catching it -at the instant the ball reaches its highest point -at the instant the falling ball hits your hands -when you hold the ball still in your hands before it is thrown

-when you hold the ball still in your hands after catching it -when you hold the ball still in your hands before it is thrown When an object's velocity is changing, the net force on it is not zero, even if it stops for an instant. Return to Assignment

Think and Rank: Three pucks, A, B, and C, are shown sliding across ice at the noted speeds. Air and ice friction forces are negligible. Part A: Rank them, from greatest to least, by the force needed to keep them moving. Rank from greatest to least. To rank items as equivalent, overlap them. A: 2 m/s -> B: 4 m/s ---> C: 6 m/s ----->

Greatest: Middle: A, B, C Least:

A stubborn stump is pulled by a pair of ropes, each with a force of 200 N, but at different angles as shown. From greatest to least, rank the total force from the ropes on the stump. Rank from greatest to least. To rank items as equivalent, overlap them.

Greatest: B Middle: C Least: A

Think and Rank: Three pucks, A, B, and C, are shown sliding across ice at the noted speeds. Air and ice friction forces are negligible. Part B: Rank them, from greatest to least, by the force needed to stop them in the same time interval. Rank from greatest to least. To rank items as equivalent, overlap them. A: 2 m/s -> B: 4 m/s ---> C: 6 m/s ----->

Greatest: C Middle: B Least: A

Think and Rank: The weights of Burl, Paul, and the scaffold produce tensions in the supporting ropes. Rank the tension in the left rope, from most to least, in the three situations, A, B, and C. Rank the tension in the left rope, from most to least. To rank items as equivalent, overlap them.

Most: C Middle: B Least: A

The force of friction on a sliding object is 10 N. The applied force needed to maintain a constant velocity is a.) 10 N. b.) less than 10 N. c.) more than 10 N.

a.) 10 N.

What was the greatest discovery by Galileo during his inclined-plane experiments? a.) He discovered that a ball rolling down an incline and onto a horizontal surface would roll indefinitely. b.) He discovered that balls rolling down an incline gain speed and balls rolling up an incline lose speed. c.) He discovered that light and heavy objects gain the same speed when rolling on inclines. d.) He discovered that heavy objects roll faster than light objects on an incline.

a.) He discovered that a ball rolling down an incline and onto a horizontal surface would roll indefinitely.

If you push on a crate with a horizontal force of 100 N and it slides at constant velocity, what is the magnitude and direction of the frictional force acting on the crate? a.) The frictional force on the crate is 100 N opposite the direction of motion. b.) The frictional force on the crate is zero newtons. c.) The frictional force has nothing to do with you pushing on the crate. d.) The frictional force on the crate is 100 N in the same direction as the direction of motion.

a.) The frictional force on the crate is 100 N opposite the direction of motion.

What is the net force on a cart that is pulled to the right with 100 pounds of force and to the left with 30 pounds of force? a.) The net force is 70 pounds to the right. b.) The net force is 70 pounds to the left. c.) The net force is zero. d.) The net force is 130 pounds.

a.) The net force is 70 pounds to the right.

Part C: Some alphabet letters are floating in a bowl of soup. You want to move a letter that is far away from you closer to you. How could you rotate the bowl to do that? a.) Unfortunately, neither rotating the bowl clockwise nor rotating it counterclockwise will work. b.) Rotate the bowl counterclockwise. c.) Rotate the bowl clockwise. d.) Rotate the bowl either clockwise or counterclockwise, depending on where the letter is located.

a.) Unfortunately, neither rotating the bowl clockwise nor rotating it counterclockwise will work.

Part C: An elevator moves straight upward at a constant speed. Newton's first law predicts that the net force acting on the elevator will _____. a.) be zero b.) point upward c.) be increasing

a.) be zero An object moving in a straight line at constant speed has zero acceleration because the net force acting on it is also zero.

Part B: According to Newton's first law, when the net force acting on an object is zero, the object must _____. a.) have constant velocity b.) be speeding up c.) be slowing down d.) have zero velocity

a.) have constant velocity When the net force is zero, the acceleration is zero, so the velocity must be constant. Note that zero velocity is simply a special case of constant velocity.

If your automobile runs out of fuel while driving, the engine stops. You don't come to an abrupt stop due to a.) inertia. b.) gravity. c.) resistance. d.) the principle of continuation.

a.) inertia.

A pair of wires support a heavy painting. Tension in the wires is greater when they are a.) not vertical. b.) the same regardless of the wire orientation. c.) vertical. d.) none of the above

a.) not vertical.

The net force on any object in equilibrium is a.) zero. b.) less than its weight. c.) non-zero when motion is involved. d.) equal to its weight.

a.) zero.

What did Galileo discover in his legendary experiment on the Leaning Tower of Pisa? a.) Galileo found that air resistance significantly slowed falling stones. b.) Galileo found that a heavier stone does not fall significantly faster than a lighter one. c.) Galileo found that stones fall faster proportional to their weight. d.) Galileo found that a heavier stone falls significantly faster than a lighter one.

b.) Galileo found that a heavier stone does not fall significantly faster than a lighter one.

What is inertia? a.) Inertia explains why things stay at rest but not why they stay in motion. b.) Inertia is the tendency of a body to maintain its state of motion in the absence of applied forces. c.) Inertia explains why things stay in motion but not why they stay at rest. d.) Inertia describes why it is easier to get a massive ball moving than it is to get a less massive one moving.

b.) Inertia is the tendency of a body to maintain its state of motion in the absence of applied forces.

Part A: Dr. Hewitt has clay "blobs" hanging on either side of his head in this video. When he turns around, what happens to the blobs? a.) The blobs fall off Dr. Hewitt's head. b.) The blobs tend to stay where they were. c.) The blobs turn around in the same direction as Dr. Hewitt. d.) The blobs turn around in the opposite direction from Dr. Hewitt.

b.) The blobs tend to stay where they were.

What is the net force on a bag pulled down by gravity with a force of 18 newtons and pulled upward by a rope with a force of 18 newtons? a.) The net force is 25 newtons. b.) The net force is zero newtons. c.) The net force is 18 newtons. d.) The net force is 36 newtons.

b.) The net force is zero newtons.

What is the net force on an object in either static or dynamic equilibrium? a.) The net force is equal and opposite to the weight of the object. b.) The net force is zero. c.) The net force is zero for static equilibrium and greater than zero for dynamic equilibrium. d.) The net force is vertical for static equilibrium and horizontal for dynamic equilibrium.

b.) The net force is zero.

When you stand at rest on a bathroom scale, how does your weight compare with the support force from the scale? a.) The support force from the scale is half your weight. b.) Your weight is equal in magnitude and opposite in direction to the support force from the scale. c.) Your weight is equal in magnitude and in the same direction as the support force from the scale. d.) The support force from the scale is twice your weight.

b.) Your weight is equal in magnitude and opposite in direction to the support force from the scale.

Part A: Recall the portion of the video in which the girl pushes her brother on the sled at constant velocity. The pushing force she exerts on the sled is _____ the frictional force the ground exerts on the sled. a.) less than b.) equal to c.) greater than

b.) equal to Because the sled's velocity is constant, the net force must be zero and the two horizontal forces must balance out.

Galileo taught us that if you roll a ball along a level surface it will a.) roll as long as its inertia nudges it along. b.) keep rolling if friction is absent. c.) soon roll in the opposite direction. d.) soon slow down due to its natural place.

b.) keep rolling if friction is absent.

While you are standing in the aisle of a bus, the driver suddenly makes a left turn. You lurch to the right due to: a.) an equilibrium challenge. b.) your tendency to keep moving forward. c.) an unbalanced force.

b.) your tendency to keep moving forward.

What is the net force when a pair of 5-N forces simultaneously act in the same direction on an object? a.) 7.5 N b.) 0 N c.) 10 N d.) 5 N

c.) 10 N

Consider a book that weighs 15 N at rest on a flat table. How many newtons of support force does the table exert on the book? a.) 30 newtons up b.) 15 newtons down c.) 15 newtons up d.) 0 newtons

c.) 15 newtons up

Burl and Paul have a total weight of 1300 N. The tensions in the supporting ropes that support their scaffold add to 1700 N. The weight of the scaffold itself must be a.) 500 N. b.) 300 N. c.) 400 N. d.) 600 N.

c.) 400 N.

What are the units for force? a.) Force must be measured in newtons; it can never be measured in pounds. b.) Force must first be measured in newtons, then converted to pounds. c.) Force can be expressed in newtons or pounds. d.) Force must be measured in pounds and then converted to newtons.

c.) Force can be expressed in newtons or pounds.

What did Galileo discover about moving bodies and force in his experiments with inclined planes? a.) Bodies rolling up an inclined plane sped up. b.) Bodies rolling down a steep inclined plane starting at a given height rolled up a gently inclined plane to a higher height. c.) In the absence of a retarding force, a body will keep moving at a constant speed in a straight line forever. d.) Bodies rolling down an inclined plane slowed down.

c.) In the absence of a retarding force, a body will keep moving at a constant speed in a straight line forever.

What type of path does a moving object follow in the absence of a force? a.) It follows a circular path in the absence of a force. b.) It moves in a straight line and eventually slows to a stop. c.) It continues to move in a straight line at a constant speed. d.) It follows a parabolic trajectory in the absence of a force.

c.) It continues to move in a straight line at a constant speed.

Consider Nellie hanging at rest in Figure 2.11. If the ropes were vertical, with no angle involved, what would be the tension in each rope? a.) The tension in each rope would be twice the gravity force. b.) The tension in each rope would be equal to the gravity force. c.) The tension in each rope would be half of the gravity force. d.) The tension would be zero in both ropes.

c.) The tension in each rope would be half of the gravity force.

Part B: Why do the clay blobs do what they do when Dr. Hewitt turns around? a.) Dr. Hewitt is turning them back to their original position. b.) Friction with the head is keeping them there. c.) They have inertia−−the tendency of an object at rest to stay at rest. d.) Dr. Hewitt is holding them there.

c.) They have inertia−−the tendency of an object at rest to stay at rest.

Part D: Why do the alphabet letters tend to do what they do when you rotate the bowl? a.) The sides of the soup bowl prevent the letters from moving. b.) The soup prevents the letters from moving. c.) They have inertia−−the tendency of an object at rest to stay at rest. d.) The letters are heavier than the soup, so they cannot move even though the soup moves.

c.) They have inertia−−the tendency of an object at rest to stay at rest.

~When you quickly jerk a cart forward that has a ball resting in the middle, the a.) front of the cart hits the ball. b.) neither, for the ball rides along in the middle as the cart moves forward. c.) back of the cart hits the ball. d.) All of the above depending on how quickly the cart is pulled.

c.) back of the cart hits the ball.

When Nellie Newton hangs by the ends of a rope draped over a large pulley, the tension in each supporting vertical strand is a.) equal to her weight. b.) twice her weight. c.) half her weight. d.) none of the above

c.) half her weight.

A hockey puck sliding at constant velocity across the ice is a.) is nowhere near being in equilibrium. b.) nearly in equilibrium. c.) in equilibrium. d.) none of the above

c.) in equilibrium.

A hockey puck sliding across the ice finally comes to rest because a.) it seeks its proper and natural state. b.) that's just the way it is. c.) of friction.

c.) of friction.

*Galileo's use of inclined planes allowed him to effectively a.) eliminate friction. b.) eliminate all changes in speed. c.) slow down the ball's changes in speed. d.) reduce the time of the ball's changes in speed.

c.) slow down the ball's changes in speed.

Why do we say that force is a vector quantity? a.) A force has a magnitude, but not a direction. b.) A force is a scalar quantity. c.) A force is measured in pounds, and pounds are a vector quantity. d.) A force has a magnitude and a direction.

d.) A force has a magnitude and a direction.

What does it mean to say something is in mechanical equilibrium? a.) An object in mechanical equilibrium experiences a net force twice its weight. b.) An object in mechanical equilibrium must experience no forces. c.) An object in mechanical equilibrium is always in motion. d.) An object in mechanical equilibrium experiences a zero net force.

d.) An object in mechanical equilibrium experiences a zero net force.

When a pair of 10-N forces act on a box of candy, the net force on the box is a.) zero. b.) about 14 N. c.) 20 N. d.) Any of the above depending on the directions of forces.

d.) Any of the above depending on the directions of forces.

How does Newton's first law of motion relate to Galileo's concept of inertia? a.) Newton replaced Galileo's concept of inertia with his three laws of motion. b.) Newton expressed Galileo's concept of inertia with the inertia equation. c.) Newton's first law of motion refuted Galileo's concept of inertia. d.) Newton refined Galileo's concept of inertia and made it his first law of motion.

d.) Newton refined Galileo's concept of inertia and made it his first law of motion.

According to the parallelogram rule, what quantity is represented by the diagonal of a constructed parallelogram? a.) The diagonal is the difference of two vectors. b.) The diagonal is 1.41 times the magnitude of the longest vector. c.) The diagonal is always 1.41 times the magnitude of the sum of the vectors. d.) The diagonal is the resultant, or sum, of two vectors.

d.) The diagonal is the resultant, or sum, of two vectors.

Part B: When Dr. Hewitt pulls the tablecloth, why do the items on the tablecloth do what they do? a.) They are attached to the tablecloth. b.) Friction with the tablecloth is keeping them there. c.) Friction with the table is keeping them there. d.) Their inertia is sufficient to keep them there.

d.) Their inertia is sufficient to keep them there.

Part A: When Dr. Hewitt pulls the tablecloth, what happens to the items on the tablecloth? a.) They move horizontally in the opposite direction from the tablecloth. b.) They move vertically upward. c.) They move horizontally in the same direction as the tablecloth. d.) They tend to stay where they were.

d.) They tend to stay where they were.

A bowling ball at rest is in equilibrium. Is the ball in equilibrium when it moves at constant speed in a straight-line path? a.) The bowling ball is not in equilibrium because it is moving. b.) The bowling ball is not in equilibrium because ΣF = -mg. c.) The bowling ball is not in equilibrium because the wood of the bowling alley exerts an upward force on the ball. d.) Yes, the bowling ball is in equilibrium because ΣF = 0.

d.) Yes, the bowling ball is in equilibrium because ΣF = 0.

Part C: You tell your friend about the neat tablecloth trick that Dr. Hewitt demonstrated. Your friend tries to repeat this trick at home and later complains to you that it failed. Which of the following is most likely the reason that it failed? a.) Your friend pulled the tablecloth too quickly. b.) The items placed on the tablecloth were too light. c.) Your friend is too clumsy. d.) Your friend pulled the tablecloth too slowly.

d.) Your friend pulled the tablecloth too slowly.

What is the net force on a crate sliding at an unchanging speed when pushed with a steady force of 75 N? a.) 75 N b.) Slightly more than 75 N c.) Somewhat less than 75 N d.) Zero

d.) Zero

A hockey puck is set in motion across a frozen pond. If ice friction and air resistance are neglected, the force required to keep the puck sliding at constant velocity is a.) equal to its mass times its weight. b.) equal to its weight. c.) equal to its weight divided by its mass. d.) none of the above

d.) none of the above

Which of the following is a vector quantity? a.) mass b.) area c.) volume d.) none of the above

d.) none of the above

State the equilibrium rule for forces in symbolic notation a.) ΣF = net force b.) ΣF = 2 mg c.) ΣF = -mg d.) ΣF = 0

d.) ΣF = 0

Consider the video demonstration that you just watched. Which of the following changes would make it more likely for the ball to hit both the white can and the green can? a.) Roll the ball slower. b.) Roll the ball faster. c.) Use a ball that is lighter than the original ball, but still heavier than an empty can. d.) Use a ball that is heavier than the original ball. e.) None of the above

e.) None of the above By Newton's 1st law, after it has left the circular track, the ball will travel in a straight line until it is subject to a nonzero net force. Thus, the ball can only hit the white can, because that is the only can in the ball's straight-line path.