kines 101 quizzes 1-3

During a bench press while a barbell (weight = 1000 N) is moving downward, an 1200 N upward force is applied with the hands to the barbell to slow it down. If no other forces are being applied to the barbell at this time, what is the acceleration of the barbell? (Round your answer to the nearest 0.01 m/s2) 0.98 m/s2, up 1.96 m/s2, up 11.77 m/s2, up 9.81 m/s2, down

1.96 m/s2, up - From the previous question, we know that the net external force on the barbell is 200 N up. To find the acceleration, we'll use the 2nd Law: F_net = ma. We're not given the mass of the barbell, but we do know its weight (1000 N). Since W = mg, we can find the mass as m = 1000 / 9.81 = 101.9 kg. Using a = F / m = 200 / 101.9 gives a = 1.96 m/s/s. The net force is up, so the acceleration is up.

At one instant during a training run, a 70 kg runner's instantaneous velocity is 5.5 m/s in the forward direction. What is the runner's kinetic energy at this instant? Give your answer to the nearest 1 J. 385 J 687 J 1059 J None of the above answers is correct.

1059 J - Kinetic energy depends on velocity and is equal to KE = 0.5 m v2, so for this runner, KE = 0.5 * 70 * (5.5)2 = 1059 J

A 93 kg football player is hit by a tackler who drives him to the right with a force of 1175 N. If the feet of the player who was hit are off the ground so we can neglect ground reaction force, what is the player's horizontal acceleration? Round your answer to the nearest 0.1 m/s/s. 21.7 m/s/s 12.6 m/s/s 18.0 m/s/s None of the above are correct.

12.6 m/s/s - Use F = ma, so 1175 = 93a and a = 12.6 m/s/s.

The frictional (tangential) force applied to the foot of a runner is 300 N, directed posteriorly. At the same time an upward normal force of 1490 N acts on the same foot. What is the magnitude of the resultant (vector sum) of these two forces acting on the foot? Give your answer to the nearest 1 N. 1503 N None of the above answers are correct. 1490 N 1520 N

1520 N - To solve this problem, we need to add the two forces. Because one is horizontal and one is vertical, we have to add them like vectors. This is done by making a right triangle with legs equal to 300 and 1490 and then we use Pythagorean Theorem to solve for hypotenuse, which is the vector sum (or "resultant").

A 10 kg plate slips off a barbell and falls to the floor, striking the floor with a velocity of 5.6 m/s, directed straight down. If the plate started with an initial velocity of zero, how far did it fall before hitting the floor? You can neglect the effects of air resistance here. Round your answer to the nearest centimeter. (Hint: You can use conservation of energy to solve this problem) 87 cm 112 cm 160 cm 213 cm

160 cm - Very similar to the diver problem we did in class. We're assuming wind resistance does no work on the diver, so energy is conserved and the gain in KE will be equal to the loss in GPE: EnergyTOP = EnergyBOTTOM 0.5 m vTOP2 + m g hTOP = 0.5 m vBOTTOM2 + m g hBOTTOM We can say vTOP = 0 and hBOTTOM = 0, so (canceling m on both sides) g hTOP = 0.5 vBOTTOM2 With vBOTTOM = 5.6 m/s and g = 9.81 m/s2, we get hTOP = 1.60 m = 160 cm

A 67 kg diver falls through a vertical distance of 3 m. How much does his gravitational potential energy change during the fall? Give your answer to the nearest 1 J. 0 J 657 J 1972 J None of the above answers is correct.

1972 J - The gravitational potential energy of a body depends on its height and is given by GPE = mgh. If we take h=0 at the end and h=3 m at the start then the change in GPE = 67 x 9.81 x 3 = 1972 J.

During a bench press while a barbell (weight = 1000 N) is moving downward, an 1200 N upward force is applied with the hands to the barbell to slow it down. If no other forces are being applied to the barbell at this time, what is the net (total) external force applied to the barbell? 200 N, up 200 N, down 2200 N, up 1200 N, up

200 N, up - These two forces tend to cancel each other out leaving a net force of 200 N up.

How far would you walk if you started at Rec Hall and walked straight down Curtin Road to the Bryce Jordan Center (that is, from one end of the PSU campus to the other)? 200 cm 2 m 2000 m 2000 cm

2000 m - 2000 m is 2 km (about 1.2 miles) and this is the only answer that makes sense. Someone who is 2 m tall is about 6'6". There are 100 cm in a meter, so if you converted 2000 cm, it would be 20 m. 200 cm is 2 m.

A golf ball is hit off the tee with a velocity of 50 m/s at an angle that is 30 degrees above the horizontal. What is the magnitude of the vertical component of the ball's velocity? Give your answer to the nearest 0.1 m/s. 20.0 m/s 25.0 m/s None of the above answers is correct. 14.8 m/s

25.0 m/s - To solve this, we have to "resolve" (break up) the velocity vector into its horizontal and vertical components. To do this, you draw a right triangle and make the original vector the hypotenuse, then find the legs of the triangle. If you draw the correct right triangle you'll have sin(30) = Vy/50.

At one instant during walking, a 90 kg subject's horizontal acceleration is measured to be 0.3 m/s/s, directed posteriorly. What is the net horizontal ground reaction force applied to the feet (i.e., the sum of the foot forces) at this time? Give your answer to the nearest 1 N. 27 N, directed posteriorly 36 N, directed posteriorly 45 N, directed posteriorly None of these answers is correct.

27 N, directed posteriorly - Remember that only horizontal forces cause horizontal accelerations. Contact with the ground is the only source of horizontal force. Use the 2nd Law: Fnet = ma. Choosing posterior to be negative, Fnet = (90)(-0.3) = -27 N The negative sign means that the 27 N is directed posteriorly. What if we had chosen posterior to be positive? This would make the given acceleration positive: Fnet = (90)(0.3) = +27 N The positive sign means that the 27 N is directed posteriorly (same as before) because this time positive means posterior.

When a man holds a dumbbell with his arms outstretched to the side (that is, with the arm parallel to the floor), the adducting moment applied to the arm by gravity is 120 Nm. If the deltoid muscle is the only muscle holding up the arm by providing an opposing abduction moment of 120 Nm (see figure below), and the deltoid's moment arm about the shoulder joint is 3 cm, what is the force F generated by the deltoid muscle? 3200 N 3600 N 4000 N None of the above answers are correct.

4000 N - The arm and the dumbbell are held in place, so this is a situation in which the acceleration of the arm is zero. This means that the moment due to the gravity force (tending to adduct the arm) is balanced by the muscle force (that tends to abduct the arm). We are told that the gravity moment is 120 N m, so this must be the muscle moment as well (as stated in the question). Moment of force is given by M = F d, and we are told that the muscle moment is M = 120 N m. The moment arm of the muscle force is d = 3 cm = 0.03 m, so F = 120 / 0.03 = 4000 N.

A hockey puck with mass 112 g is contacted by the blade of a hockey stick, which applies a rightward force of 900 N to the puck. What force is applied to the blade of the stick by the puck? Round your answer to the nearest 1 N. 900 N, directed to the right 0 N, no force is applied to the stick by the puck 1099 N, directed down 900 N, directed to the left

900 N, directed to the left - Two bodies in contact exert equal and opposite forces on one another (Newton's Third Law of Motion).

The left knee is distal to the left ankle. TRUE OR FALSE

False - "Distal to" means farther away from the center of the body, and the knee is closer to the body's center than the ankle is. You could say "the knee is proximal to the ankle" or "the ankle is distal to the knee".

A body in mechanical equilibrium cannot have any forces acting upon it. True False

False - "Equilibrium" implies that the forces acting on the body must add up to zero, but it doesn't mean that no forces can be acting. Two forces that cancel one another out could be acting and the net force would be zero. Follows from 2nd Law -> Fnet = ma. Example: a person standing still is in equilibrium but gravitational and ground contact forces act on the person.

The next 3 questions refer to a pole vaulter executing a pole vault, starting with the run up and ending just before contact with the landing mat. TRUE OR FALSE: The pole vaulter has no kinetic energy until he leaves the ground.

False - Kinetic energy is associated with motion. In an equation, KE = 0.5 m v2. Because the pole vaulter is moving (running) before he leaves the ground, he has velocity and therefore KE before he leaves the ground.

"Medial" is an anatomical term meaning "to the left" and "lateral" means "to the right". TRUE OR FALSE

False - Left-right and medial-lateral are both side-to-side directions, but they are not the same. Medial means toward the midline of the body and lateral means away from the midline in either direction. So, both of your ears are "lateral to" your brain, but your right ear is the right of your brain and your left ear is to the left of your brain.

"Compact" (or cortical) bone is the type of bone that is spongy in appearance and is light yet strong. TRUE OR FALSE

False - This is a description of trabecular (or cancellous) bone. Compact bone is solid and dense.

When someone nods their head as if to indicate "yes", they are performing a primarily "frontal plane motion" with their head and neck. TRUE OR FALSE

False - This is a sagittal plane motion - try to envision a point like the tip of the person's nose during this motion. It would stay in the sagittal plane. A frontal plane head and neck motion would be tilting your head to the side, like when a swimmer tries to get water out of their ear.

The arms of a man performing kettlebell swings (as pictured below) are rotating primarily in the transverse plane. TRUE OR FALSE

False - This is a sagittal plane motion. A mid-sagittal plane separates the left half of your body from the right half, and other sagittal planes are parallel to the mid-sagittal plane. This is a sagittal plane motion because his body parts are moving within (tracing out paths on) a sagittal plane.

If the net force acting on a body is zero, then the net moment acting on the body must also be zero. TRUE OR FALSE

False - We find the total moment acting on a body by adding up the moments due to each force acting on the body. We don't do this by finding the net force first. Here's why: Two equal and opposite forces cancel each other out, yielding zero net force, but if those forces are not collinear (acting along the same line) there will be a net moment. See lecture notes for a picture.

Muscle contraction is produced by attachments formed between the proteins actin and myosin. TRUE OR FALSE

Muscle force is produced when crossbridges form between actin and myosin, then rotate to produce translation between the sliding filament proteins.

How much work is done against gravity as a 50 kg barbell is raised from the floor to a height of 2 m above the floor, if we know that the barbell begins and ends with zero velocity? Give your answer to the nearest 1 J. 25 J 100 J 200 J None of the above answers are correct.

None of the above answers are correct. - There is an equivalence between work and energy. This means that if I do 100 J of work on a body, its energy increases by 100 J, as long as no force other than gravity (such as friction) also acts on the body. The barbell's kinetic energy is the same at the end as it is at the beginning (zero), so the work done on the barbell must be equal to the change in gravitational potential energy (GPE). Work = mghAFTER - mghBEFORE = 50 * 9.81 * 2 - 0 = 981 J You could also get this answer by noting that the average upward force F applied to barbell is equal to weight of barbell F = 50 * 9.81. This upward force will be a little greater than this at the beginning when the weight accelerates upward and a little less at the end when it slows down. Work = F d, so = (50 * 9.81) * 2 = 981 J

A hockey puck with mass 112 g is contacted by the blade of a hockey stick, which applies a rightward force of 600 N to the puck. If this force is the only horizontal force applied to the puck, find the puck's horizontal acceleration. Round your answer to the nearest 1 m/s/s. 10 m/s/s, to the right 101 m/s/s, to the right 8036 m/s/s, to the right None of the above answers are correct.

None of the above answers are correct. - Use Newton's Second Law, F = ma, which relates force and acceleration. Only one horizontal force acts, so F = 600 N. The mass is 112 g, but we need to express this in kg if acceleration is to come out in m/s/s: 0.112 kg. Solving, we get 5357 m/s/s.

A 112 g hockey puck glides across a frictionless ice surface with no horizontal forces acting on it. If the puck's velocity is 22.5 m/s to the right at t = 0 s, what will the puck's horizontal velocity be at t = 225 ms? Round your answer to the nearest 0.1 m/s. 0.0 m/s None of these answers is correct. 25.0 m/s, to the right 10.0 m/s, to the right

None of these answers is correct. - With no forces applied to it, the puck remains in uniform motion. That is, its velocity remains constant (Newton's First Law of Motion) and the velocity will be 22.5 m/s until a horizontal force acts to speed it up or slow it down.

When the pole is bent after the vaulter leaves the ground, the pole is storing elastic potential energy. TRUE OR FALSE

TRUE - A pole doesn't look like a spring but it behaves like one when it is bent and snaps back to its original shape. The energy associated with the deformation of a spring, or anything that behaves like a spring by snapping back to its undeformed position, is called elastic potential energy. For this class it's not important to know an equation for EPE, just that when materials are bent, stretched, or compressed and return to their original positions, they store and release EPE.

pole vaulter executing a pole vault, starting with the run up and ending just before contact with the landing mat. The gravitational potential energy of the vaulter is greatest when the pole vaulter reaches his peak height in the air. TRUE OR FALSE

True - Gravitational potential energy depends on the mass of the body and its height above some reference height (such as the ground). As an equation it is GPE = mgh. GPE would be greatest at the top, when h is greatest as the vaulter clears the bar.

Newton's Second Law implies that when the same net force is applied separately to two bodies that have the same mass, then the accelerations of the two bodies will be the same. False True

True - The 2nd Law says F = ma. If F = m a1 and F = m a2, then a1 must be the same as a2.

The elbow is surrounded by a capsule containing lubricating fluid. TRUE OR FALSE

True - The capsule containing fluid (synovial fluid) is a defining characteristic of a synovial joint

A body could have a net force acting on it to the right while the body's velocity is directed to the left. TRUE OR FALSE

True - The net force and the acceleration vectors must be in the same direction, but net force and velocity can be in opposite directions. For example, as you catch a ball that is dropped into your hand, the ball may move down as your hand applies an upward force to it that is greater than the ball's weight, slowing it down.

When you apply a forward-directed force to a baseball in order to throw it, the baseball exerts a backward force upon your hand. TRUE OR FALSE

True - This is a straightforward application of the 3rd Law. Any time two bodies are touching each other, the forces exerted on each body by the other are equal and opposite to each other.

In a "concentric" muscle contraction, the muscle shortens. TRUE OR FALSE

True - This is the definition of a concentric (shortening) contraction.

A "kinetic" analysis of human motion is one in which forces and motions are considered together. TRUE OR FALSE

True - This is the definition of kinetic. Kinematic analysis would be motions alone with no forces.

What is the velocity of an 80 kg skydiver who is falling with 16,000 J of translational kinetic energy? Give your answer to the nearest 1 m/s. 10 m/s 20 m/s 200 m/s 400 m/s

20 m/s - KE = 0.5 m v2 so 16000 = 0.5 * 80 * v2 v2 = 16000/40 = 400 v = 20 m/s

Guillaume Duchenne made one of the first motion pictures when he analyzed the movements of a horse's hooves. TRUE OR FALSE

False - It was Eadward Muybridge who made the photographs of a horse galloping

Mass is measured using units of newtons. TRUE OR FALSE

False - Mass is measured in kilograms (kg) and force is measured in newtons (N)

When you shake your head as if to indicate "no" in answer to a yes-no question, you are rotating your skull in the sagittal plane. TRUE OR FALSE

False - This is a transverse plane motion. Nodding your head "yes" would be a sagittal plane rotation. See lecture notes for descriptions of these planes.

The "origin" of a muscle-tendon unit refers to the location where its proximal tendon attaches to bone. TRUE OR FALSE

True - This is the definition of the "origin" of a muscle.

A man begins walking in a straight line by starting from rest (velocity of zero). By the time he has been walking for 3.0 s, his forward velocity is 1.5 m/s. What is the magnitude of the man's average acceleration during this time? None of the above answers is correct. 0.4 m/s/s 0.0 m/s/s 0.5 m/s/s

0.5 m/s/s - Average acceleration is found by dividing change in velocity by change in time. A = 1.5 / 3.0 = 0.50 m/s/s.

A patient in hand therapy completes a reaching task in which his fingertip moves 32 cm along a straight path in 400 ms. What is the fingertip's average velocity during the movement? (hint: All the answers below are in m/s, so it would be a good idea to convert centimeters (cm) to meters and milliseconds (ms) to seconds before computing velocity) 0.8 m/s 1.5 m/s 1.25 m/s None of the above answers is correct.

0.8 m/s - To find average velocity we divide displacement D by time T. To find velocity in m/s, we'll express displacement in m and time in seconds before we take the quotient. D = 32 cm = 0.32 m, and T = 400 ms = 0.400 s. Dividing, we get Vavg = 0.32 / 0.400 = 0.8 m/s.

The knee is a synovial joint. TRUE OR FALSE

True - Any joint that allows substantial movement is a synovial joint, including the hip, knee, joints in the jaw and fingers, and many more.

Just before the left foot touches the ground (when only the right foot is touching the ground) during the walking of a 67 kg subject, the vertical component of the ground reaction force (GRF) applied to the right foot is measured to be 640 N. What is the vertical component of the acceleration of the subject's center of mass? Give your answer to the nearest 0.01 m/s/s. (Hint: Draw a "free-body diagram", or FBD) 0.26 m/s/s, directed down 9.55 m/s/s, directed down 9.81 m/s/s, directed down None of these answers is correct.

0.26 m/s/s, directed down - Remember that only vertical forces cause vertical accelerations. Let's think about what the vertical forces are. Your FBD should show two vertical forces, the given vertical GRF G (an upward force) and the weight W (a downward force). Use Newton's Second Law (Fnet = ma). The net force is G - W, the GRF minus the weight, so G - mg = ma With G = 640 N and m = 67 kg, a = -0.26 m/s/s. Negative means down here because the weight, a downward force, was chosen to be negative earlier.

Which of these could be the length of a Penn State student's foot? 0.027 km 2.7 m 0.27 m 27 mm

0.27 m - See lecture notes for more information on units - 0.27 m is 27 cm (about 11 inches). All other answers are far off. If you missed this question, try converting all the answers into units you are comfortable with. Try centimeters (cm) - one cm is close to the width of your little finger.

Just before a baseball is struck by a bat, its velocity is +40.0 m/s (positive means directed away from the pitcher). Just after being hit, the ball's velocity is -60.0 m/s (negative means directed toward the pitcher). If the impact with the bat takes 200 ms, what is the magnitude of the average acceleration of the ball during the impact? (Note that you are just being asked for the magnitude of the acceleration here. This means that all you should be looking for is the size of the acceleration and not its direction. For example, the magnitude of an acceleration that is -1000 m/s is 1000 m/s, because we can ignore the negative sign that just indicates direction and not magnitude.) 400 m/s/s 500 m/s/s 200 m/s/s None of the above answers is correct.

500 m/s/s - The change in velocity is -100 m/s because the ball goes from +40 m/s to -60 m/s. This happens in 0.2 s, so the average acceleration is -100/0.2 = -500 m/s/s. The magnitude (size) of the acceleration is 500 m/s/s. What if you had been asked what the direction of the average acceleration was? You'd say that the acceleration was directed toward the pitcher. You could say this because the acceleration comes out negative and you're told negative is toward the pitcher. Or, you could reason that the velocity changes in a way that makes the ball head more toward the pitcher than away from the pitcher.

Which of the following could be the body mass of a Penn State student? 65 g None of the above answers could be correct. 65 kg 6.5 kg

65 kg - Two of the answers are way too small to be correct. You should have an idea of what object has a mass of 1 kg - the example from lecture was a 1 L bottle of water. Any PSU student's body mass would be much more than that of 6.5 bottles of water, so 6.5 kg has to be wrong. A kg is 1000 g, so 65 g is much less than the mass of even one bottle of water. One gram (1 g) is the mass of a single paper clip, or a single dollar bill. You may be comfortable enough with kg to know that 65 kg is the answer, but if you're not already comfortable with units of kg, you're probably comfortable with pounds. An object that has a mass of 1 kg weighs 2.2 pounds. To convert kg to pounds, multiply by a form of 1 (fraction equal to one) that makes kg cancel and leaves you with pounds. The form of 1 you'll use here is (2.2 lbs/1 kg), and 65 kg * (2.2 lbs / 1 kg) = 143 lbs. You could also ask Google "65 kg in lbs" to get this answer.

A pole vaulter (body mass = 70 kg) has just cleared the bar and is falling to the mat below. What is the pole vaulter's weight? Give your answer to the nearest 0.1 newtons. 0.0 N 781.0 N None of the above answers is correct. 686.7 N

686.7 N - Weight depends on body mass alone as long as we are not far from the earth. W = m g.

The frictional (tangential) force applied to the foot of a runner is 300 N, directed posteriorly. At the same time an upward normal force of 1490 N acts on the same foot. What is the angle formed between the horizontal and the vector that is the resultant (sum) of these two forces acting on the foot? Give your answer to the nearest 0.1 degrees. 89.0 degrees 11.4 degrees 78.6 degrees 45.0 degrees

78.6 degrees - To find the angles within a right triangle, we'll use the inverse tangent (atan) function. In this case, the angle with horizontal is equal to atan(1490/300) = 78.6 deg. Choice 1 is angle with vertical.

Which of the following could be the weight of an adult human male? 80,000 kN 8,000 N 800 N 80 N

800 N - 800 N is about 180 lbs. It's not necessary to memorize this conversion, but 1 lb. is 4.45 N, and you should have an idea of your own weight in newtons - this should help you to get this answer. All the other answers are too far off to be people: A garbage truck might weigh 80,000 N. A small car might weigh 8,000 N. A suitcase full of clothes might weigh 80 N.

A man rides a bicycle ergometer for 30 minutes and during this time his feet do 200,000 J of work on the pedals. Which of the following values could be the metabolic energy expended by the man (that is, the amount of energy derived from all metabolic sources) during this time? 50,000 J 100,000 J 200,000 J 800,000 J

800,000 J - We are not perfectly efficient when exercising; if we were then every bit of energy derived from food would have been delivered to the pedals (200,000 J). The first two choices are impossible because energy has come from nowhere to drive the pedals. The last choice (800,000 J) is best because it reflects an efficiency of 0.25, which is typical -- see notes.

A dumbbell is raised during a biceps curl. The upper arm is vertical and the elbow is flexed to 90 degrees. The motion is performed slowly so you can assume that the angular acceleration of the forearm is zero. You can neglect the weight of the forearm. True or false: The weight of the dumbbell held in the hand will be less than the force generated by the biceps muscle at this time. TRUE OR FALSE

TRUE - It's tempting to say that the muscle force should be larger because the dumbbell is rising, but this ignores everything we know about rotational mechanics. Both forces are acting to cause rotation at the elbow - the muscle force has a moment that is in the elbow flexion direction and the weight does the opposite by tending to make the elbow extend. The arm is moving slowly, so you're told to assume zero angular acceleration (a good assumption for a slow biceps curl) so the moments of the two forces will be equal. In an equation, we would have FB * dB - W * dW = 0 The negative sign on one of these moments accounts for the fact that these moments cause opposite rotations at the elbow. The moment arm of the weight of the dumbbell about the elbow (dW) is huge (around 30 cm) compared to the moment arm of the biceps force about the elbow (dB, about 5 cm), so the biceps force FB will be much larger than the weight W. There is an example like this in the lecture notes.

Moment of force is reported using units of newton meters (N m). TRUE OR FALSE

TRUE - Moment of force is computed as the magnitude of a force multiplied by the perpendicular distance between the force's line of action and some point about which the moment is taken. The units for moment of force (or just "moment") are thus newton meters (N m).

If you start with your right arm hanging down at your side and then perform an abduction of the right shoulder, your right arm will move within the frontal plane. TRUE OR FALSE

True

The study of anatomy was furthered during the Renaissance by artists who sought more realistic depictions of the human form. TRUE OR FALSE

True

A body in mechanical equilibrium could be moving. TRUE OR FALSE

True - "Equilibrium" means no acceleration (and therefore no net force). A body can have a nonzero velocity but have zero acceleration. As an example, think of a hockey puck gliding across a frictionless ice surface with a constant velocity.