Kinesiology 101 Biomechanics Quizzes

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

0.27m

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? 0.0m/s/s 0.4m/s/s 0.5m/s/s none of the above

0.5m/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 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. 12.6m/s/s 18.0m/s/s 21.7m/s/s none of the above

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. 1490N 1503N 1520N none of the above

1520N 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) 87cm 112cm 160cm 213cm

160cm 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 vTOP^2 + m g hTOP = 0.5 m vBOTTOM^2 + m g hBOTTOM We can say vTOP = 0 and hBOTTOM = 0, so (canceling m on both sides) g hTOP = 0.5 vBOTTOM^2 With vBOTTOM = 5.6 m/s and g = 9.81 m/s^2, we get hTOP = 1.60 m = 160 cm

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. 14.8m/s 20.0m/s 25.0m/s none of the above

25.0m/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.

Find the body mass in SI units for a patient who weighs 143 lbs. Round to the nearest kg. 65kg 82kg 398kg none of the above

65 kg An object that has a mass of 1 kg weighs 2.2 pounds. To convert pounds to kg, multiply by a form of 1 (fraction equal to one) that makes pounds cancel and leaves you with kg. The form of 1 you'll use here is (1 kg /2.2 lbs). 143 lbs * (1 kg /2.2 lbs) = 65 kg.

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 686.7N 781.0N none of the above

686.7N 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. 11.4 degrees 45.0 degrees 78.6 degrees 89.0 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.

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? 50,000J 100,000J 200,000J 800,000J

800,000J 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

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

800N 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 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. 0N, no force is applied to the stick by the puck 900N, directed to the left 900N, directed to the right 1099N, directed down

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

T or F Mass is measured using units of newtons.

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

T or F Guillaume Duchenne made one of the first motion pictures when he analyzed the movements of horse's hooves.

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

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) 0.26m/s/s, directed down 9.55 m/s/s, directed down 9.81 m/s/s, directed down none of the above

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.

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) 0.8m/s 1.25m/s 1.5m/s none of the above

0.8m/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.

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/s^2) 0.98m/s/s, up 1.96 m/s/s, up 9.81 m/s/s, down 11.77 m/s/s, up

1.96 m/s/s, 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. 385J 687J 1059J none of the above

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

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. 0J 657J 1972J none of the above

1972J 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? 200N, down 200N, up 1200N, up 2200N, up

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

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. 10m/s 20m/s 200m/s 400m/s

20m/s KE = 0.5 m v^2 so 16000 = 0.5 * 80 * v^2 v^2 = 16000/40 = 400 v = 20 m/s

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 27N directed posteriorly 36 N directed posteriorly 45 N directed posteriorly none of the above

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.

Zdeno Chára of the Boston Bruins holds the world record for the fastest slap shot, at 48.64 m/s. If, while the hockey puck is in flight, we assume that the puck has a constant velocity of 48.64 m/s along a straight line, how far will the puck travel in 750 ms? You may assume that the puck's average velocity during this time is equal to the given constant velocity. 36.48m 54.12m 64.85m none of the above

36.48m When the velocity is constant, the value of the constant velocity is identical to the average velocity. Referring to the formula for average velocity., Vavg = (x2-x1)/T. Here we are given Vavg (48.64 m/s) and T (750 ms, or 0.75 s) and need to find x2-x1. The answer is 36.48 m

When a man holds two dumbbells with arms outstretched as shown in Example 6.6 (see notes), the adducting moment applied to each 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, and the deltoid's moment arm is 3 cm, what is the force generated by each deltoid muscle? 3200N 3600N 4000N none of the above

4000N Moment of force is given by M = F d, and we are told that M = 120 N m and d = 3 cm = 0.03 m, so F = 120 / 0.03 = 4000 N.

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.) 200m/s/s 400m/s/s 500m/s/s none of the above

500m/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.

T or F A body in mechanical equilibrium cannot have any forces acting upon it.

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.

T or F The average angular velocity between point A and point E is zero. (this question refers to the graph above)

False Average angular velocity is found by computing the change in angular position and dividing by the time it takes to change position. The change in angle theta between A and E is positive (the angle at E is more positive than the angle at A), so this average angular velocity is positive. It is true that the instantaneous velocities at A and at E are both zero, but average velocity is not found by taking the average of two instantaneous velocities.

T or F A runner completing the 100 m dash in typical fashion (running in a straight line; no running start; runs through the finish line) must have an instantaneous velocity at the finish line that is twice his average velocity for the race.

False Average velocity is total displacement (change in position) divided by total time, in this case 100 m divided by the race time. It has no relation to the instantaneous velocity, which is the velocity at any one point in time.

Questions 5-7 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 v^2. Because the pole vaulter is moving (running) before he leaves the ground, he has velocity and therefore KE before he leaves the ground.

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

Questions 2 through 4 refer to the graph below showing angular position plotted versus time: True or false: The angular velocity at Point B is negative.

False The angular position (theta) is negative here, but the angular velocity is positive because the angular position is getting more positive at B, and velocity describes how position changes over time.

The above figure shows the horizontal displacement (position) plotted versus time for a hiker who walks along a straight path (displacement is relative to the hiker's base camp location). True or false: The hiker's velocity at point D is zero.

False The position is zero at D, but the velocity (indicated by the slope) is negative. You can tell this because the position is becoming more negative at D.

The above figure shows the horizontal displacement (position) plotted versus time for a hiker who walks along a straight path (displacement is relative to the hiker's base camp location). True or false: At none of the labeled points (A - D) is the velocity negative.

False The velocity is negative at points C and D. At both C and D the position is becoming more negative, and this is the definition of a negative velocity. Another way to think of this is to consider the slope of the tangent to the curve (the line that just "kisses" the curve) at C and D. In both cases the tangents slope downward from left to right. Can you tell where the velocity is most negative - at C or D? It's more negative at D because the downward slope is more negative there. The position is getting negative faster at D than at C.

The above figure shows the horizontal displacement (position) plotted versus time for a hiker who walks along a straight path (displacement is relative to the hiker's base camp location). True or false: At exactly three of the labeled points (A - D) the velocity is positive.

False The velocity is not positive at any of the labeled points. A positive velocity would be represented by a positive slope (a curve that climbs from left to right), and that is not true at A, B, C, or D. It is true that the position x is positive at A, B, and C, but this question asked about velocity and not position.

The above figure shows the horizontal displacement (position) plotted versus time for a hiker who walks along a straight path (displacement is relative to the hiker's base camp location). True or false: The hiker's velocity is zero at exactly one (that is to say: at one and only one) of the four labeled points (A - D).

False The velocity is zero at two points, A and B. We know this because the slope of the curve is zero there (because position is not changing with time at either point).

T or F The arms of a man performing kettlebell swings (swinging through legs, going up and down) are rotating primarily in the transverse plane.

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.

T or F 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.

False This is a transverse plane motion. Nodding your head "yes" would be a sagittal plane rotation.

T or F A runner's forward velocity may be expressed in meters per second squared.

False Velocity is change in position (measured in m) divided by the time it takes to change position (measured in s), so the units of velocity will be m/s. You would measure how fast velocity changes (also called acceleration) using meters per second squared. Another way to think of this is that acceleration is an expression of how many meters per second your velocity changes by every second. This is meters per second per second, or meters per second squared.

T or F If the net force acting on a body is zero, then the net moment acting on the body must also be zero.

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

T or F Henry Gray published a classic anatomy text in 1858.

True

T or F 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 be confined to the front plane.

True

T or F In an "concentric" muscle contraction, the muscle shortens.

True

T or F The "origin" of a muscle-tendon unit refers to the location where its proximal tendon attaches to bone.

True

T or F The study of anatomy was furthered during the Renaissance by artists who sought more realistic depictions of the human form.

True

T or F A body in mechanical equilibrium could be moving.

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.

T or F When the pole is bent after the vaulter leaves the ground, the pole is storing elastic potential energy.

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.

T or F The gravitational potential energy of the vaulter is greatest when the pole vaulter reaches his peak height in the air.

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.

T or F 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 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.

T or F Muscle contraction is produced by attachments formed between the proteins actin and myosin.

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

T or F The instantaneous angular velocity is positive at point C. (this question refers to the graph above)

True The curve has an upward (positive) slope at C, indicating that the instantaneous angular velocity is positive. Note that the instantaneous angular velocities at B, C, and D are all the same - you can tell this because they all lie on the same straight line that has the same slope at B, C, and D.

T or F A body could have a net force acting on it to the right while the body's velocity is directed to the left.

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.

T or F 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 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.

T or F Moment of force is reported using units of newton meters (N m).

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).

T or F The right elbow is proximal to the right wrist.

True. "Proximal to" means closer to the center of the body, and the elbow is closer to the body's center than the wrist is. It is also true to say that the wrist is distal to the elbow.

T or F For a runner completing the 100 m dash in typical fashion, the instantaneous acceleration could be zero one second before the runner finishes the race.

True. Zero acceleration signifies a constant velocity, and it's possible that the runner's forward velocity is not changing late in the race. It's also possible that the velocity is decreasing, which would be a backward acceleration (or a negative acceleration if we say that forward means positive). Be careful about confusing acceleration (how fast velocity is changing) with velocity. A runner can have a zero acceleration without having zero velocity.

T or F The hip s a synovial joint.

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

T or F The elbow is surrounded by a capsule containing lubricated fluid.

True. the capsule containing fluid, the synovial fluid, is a defining characteristic of a synovial joint.

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. 25J 100J 200J none of the above

none of the above 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

none of the above 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. 0.0m/s 10.0m/s, to the right 25.0m/s, to the right none of the above

none of the above 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.