Exam 1

Explain Newton's second law

(law of acceleration) acceleration is proportional to force and the object will accelerate in the direction of the force

What work is done by friction on a 30 kg crate that slides along a level surface beginning until it stops if its initial velocity was 6.0 m/s?

- 540 J

At max height what does velocity=

0 m/s

The mass of an official basketball for women is 567 grams. How much does a women's basketball weigh in pounds?

1.25 lb.

If you run a mile, how many meters have you run?

1609 m

In the Winter Olympic sport of curling, the rock's mass is 18 kg. What is the rock's weight in pounds?

40 lb.

How many yards are there in a 400 m track?

437 yd

Fitness instructor Kim weighs 491 N. What is her mass?

50 kg

What is the magnitude of the dynamic frictional force when pulling on a 35.0 kg crate along a level surface with a horizontal 200N force if the coefficient of kinetic friction is 0.55?

Fd= 188.9 N

Explain why the application of a large force will not ensure a large power output

Because power is Fv and regardless of how big the force is if the velocity is low the power could be low also

Compute the frictional force for an object that is 50 kg that is stationary on a slope of 15 degrees

F= 127 N

to find the resultant force use

Pythagorean theorem

During an ice hockey game, Phil had two shots on goal—one shot from 5 m away at 10 m/s and one shot from 10 m away at 40 m/s. Which shot did Brian, the hockey goalie, have a better chance of blocking?

The shot from 5 m away will take 0.50 s to reach the goal, while the shot from 10 m away will take 0.25 s to reach the goal. The goalie will have a better shot at blocking the 5 m shot.

Can an object be accelerating if the sum of the forces that are acting on it are zero?

Think of F=ma; if F= 0 then acceleration has to be zero

What is inertia?

a body's resistance to change in motion

Torques change with ______ ________

joint angles

What does the 'k' stand for in the equation for potential elastic energy?

k stands for the stiffness of a material. the more a material is able to deform, the greater the strain energy

Kinematics and kinetics are under what

rigid body DYNAMICS

Human movement is caused by _____ produced by muscular contractions

torques

T or F COM/ COG is a fixed point

false; it can change with movement

T or F the total mechanical energy of a projectile changes throughout flight

false; it remains the same throughout flight

What is torque

force that causes something to rotate

What is an eccentric force?

force that foes outside the center of mass

What is a centric force?

force that goes through the center of mass

potential energy is dependent on _____

height

in elastic collisions the ____ velocity of one object will be the same as _____ velocity of other object

initial; final

What are the goals of sports biomechanics?

injury prevention and improvement of performance

How do we classify forces?

internal forces and external forces

What is a 2nd class lever?

load in middle, axis on end, force on other end - mechanical advantage - most tools

What is a 3rd class lever?

load on one end, force in middle, axis on other end - speed advantage - most levers in body

What is a vector

magnitude and direction

stability and ______ are an inverse relationship

mobility

What is COM

most balanced point of mass within an object

In order for there to be mechanical work theres has to be what

movement (displacement)

static friction= point

of impending motion

What is an internal force and what are some examples

originate and terminate within body (compression, tension)

In P=Fv, force and velocity have to be ______

parallel

What is the coefficient of restitution

ratio of final to initial relative velocity between 2 objects after they collide - ranges from 0-1 (1 would be a perfectly elastic collision)

Amy is in a tuck and skiing straight down a 30° slope. Air resistance pushes backward on her with a force of 10 N. The coefficient of dynamic friction between her skis and the snow is 0.08. Amy's mass is 60 kg. What is the resultant of the external forces that act on Amy?

resultant force= 244 N down the hill parallel to 30 degree slope

Is distance scalar or vector?

scalar; length is path

What is kinetics?

study of forces that cause motion

What is kinematics?

study of motion

What are the 2 classifications of motion?

translational and rotational

T or F all projectiles have the same accleration

true (-9.81 m/s^2)

A ball is dropped from a height of 10 meters. When it bounces off the ground it leaves the ground with an upward velocity of 12 m/s. What is its coefficient of restitution?

0.857

How high will a soccer ball rise if it is kicked so that it stays airborne for 3 seconds?

11.1 m

Katie exerts a 400 N upward force on a 700 N barbell that is resting on the floor. The barbell does not move. How large is the normal contact force exerted by the floor on the barbell?

300 N or 150 N at each plate

Which bowling ball has more energy, a 5 kg ball rolling at 4 m/s or a 6 kg ball rolling at 3 m/s?

5 kg ball rolling at 4m/s (40 J vs 27 J)

How many miles in 100 km?

62.2 mi

A 0.15 kg baseball collides with a 1.0 kg bat. The ball has a velocity of 40 m/s immediately before the collision. The center of mass of the bat also has a velocity of 40 m/s, but in the opposite direction, just before the collision. The coefficient of restitution between the bat and the ball is 0.50. Estimate how fast the baseball is moving as it leaves the bat following the collision.

64 m/s

Mairin is a 55 kg road cyclist. Her bicycle weighs 100 N. What is the combined weight of Mairin and her bicycle?

640 N

In 1993, Javier Sotomayor of Cuba set the high jump world record by clearing a height of 2.45 m. How high is that in feet and inches?

8 ft 2.5 in

The patellar tendon attaches to the tibia at the tibial tuberosity. The tibial tuberosity is 7 cm from the center of the knee joint (a). The patellar tendon pulls at an angle of 35° to a line passing through the tibial tuberosity and the center of the knee joint. If the patellar tendon produces an extension torque around the knee joint equal to 400 Nm, how large is the force in the patellar tendon?

9963 N

A person is lifting weights and is raising a weight upward at a constant rate of 1 m/s (the weight is already moving). If the weight weighs 200 N, how much force does the person have to push the weight with to maintain the upward velocity of 1 m/s?

= 200 N because it is already moving. If we were starting the movement (the weight is stationary) then it would have to be > 200 N ?

Billy is trying to slide an 80 kg box of equipment across the floor. The coefficient of static friction between the box and the floor is 0.55. If Billy pushes only sideways (horizontally) against the box, how much force must he push with to initiate movement of the box?

> 432 N

What is a scalar quantity?

A quantity that has only magnitude

A barbell is loaded with two 20 kg plates on its right side and two 20 kg plates on its left side. The barbell is 2.2 m long, and its unloaded mass is 20 kg. The two 20 kg plates on the right side are locked in place at 35 cm and 40 cm from the right end of the bar. The two 20 kg plates on the left side have slipped. One is 30 cm from the left end of the bar, and the other is 20 cm from the left end of the bar. Where is the center of gravity of this barbell with the four plates?

COG is 115 cm to the left of the right end of the barbell (105 cm to the right of the left end of the barbell or 5 cm to the left of the center of the bar)

free weights vs machines

Free weights are better in that the world is a 'free weight situation' (principle of specificity); they resemble the human condition better - better for athletic events machines better in rehab world

A person with a 85 kg mass is pushing on a wall with a force of 500 N. The person pushes for 10 seconds. The wall does not move. How much work did the person perform?

None because U=Fd and there was no displacement. Work requires movement

Daisy walks across a force platform, and the forces exerted by her foot during a step are recorded. The peak vertical reaction force is 1200 N (this force acts upward on Daisy). At the same instant, the braking frictional force is 200 N (this force acts backward on Daisy). a. How large is the resultant of these forces? b. What is the direction of the resultant force?

a. 1217 N b. the force acts upward and backward at an angle of 80.5 degrees

A baseball batter sets up in the batting box and holds his bat still over the plate for a moment. The batter holds the 0.91 kg bat in a horizontal position with only one hand. The hand is 10 cm from the knob end of the bat. The bat is 89 cm long, and its center of gravity is 60 cm from the knob end of the bat. a. How large is the vertical force exerted by the batter's hand on the bat? b. How large is the torque exerted by the batter's hand on the bat?

a. 8.9 N b. 0.445 Nm

Brian is attempting to high jump over a crossbar set at 2.44 m (8 ft). At the instant of takeoff (when he is no longer in contact with the ground) his vertical velocity is 4.0 m/s, and his center of gravity is 1.25 m high. a. What is Brian's vertical acceleration at the instant of takeoff? b. How much time elapses after takeoff until Brian reaches his peak height? c. What peak height does Brian's center of gravity achieve?

a.9.81 m/s^2 downward b. 0.41 s c. 2.07 m

What is an external force and what are some examples??

act on an object as a result of its interaction with the environment surrounding it. (contact and noncontact) - Contact (most): normal, frictional - non contact: gravitation

What is rotational motion?

also called angular motion- particles all rotate with respect to a given axis

What is a 1st class lever

axis is in middle, load on one end, force on the other end (teeter totter)

For work, force and distance have to what

be in the same direction

What is COG

center point of where gravity is affecting object

What is impulse

change in momentum (area under the F vs t curve) - net impulse represents sum of both positive and negative areas

Explain what 'd' stands for in U=Fd and T=Fd

d stands for displacement in both. However, in U=Fd force and displacement have to be parallel to each other and in T=Fd displacement has to be perpendicular to force

Newton's 3rd law

(law of action- reaction) For every action force there is an equal and opposite reaction force - forces come in pairs and each force in a pair act on a separate object - "big guy hits little guy and both experience the same force"

Newton's 1st law

(law of inertia) An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force. - moving at constant velocity= 0 = equilibrium so no acceleration!!!!

what angle is optimum for mirror image projectiles? what angles is optimum if the landing higher than the start? what angles is optimum if the landing lower than the start?

- 30 degrees - > 45 degrees - < 45 degrees

What is negative work?

- Motion and force in opposite directions - body doing work on a force (like lowering a weight or catching a ball)

The magnitude of friction depends on what 3 factors?

- weight (normal friction) - coefficient of friction - are the surfaces moving relative to one another

What goes into the observation component of qualitative biomechanical analysis

- who - what conditions (competition) - where to observe - what to look for - other senses - must be planned in advance

1 N =

1 kg m/s^2

What are the 3 ways to correct errors in qualitative biomechanical analysis?

1. major to minor 2. earliest to latest 3. easiest to most difficult

How long does an object have to fall to reach a speed of 13 m/s?

1.33 s

A sprinter is just coming out of the starting block, and only one foot is touching the block. The sprinter pushes back (horizontally) against the block with a force of 800 N and pushes down (vertically) against the block with a force of 1000 N. a. How large is the resultant of these forces? b. What is the direction of the resultant force?

a. 1281 MN b. force acts downward and backward on the blocks at angle of 51 degrees

Sam receives the kicked football on the 3 yd line and runs straight ahead toward the goal line before cutting to the right at the 15 yd line. He then runs 9 yd along the 15 yd line directly toward the right sideline before being tackled. a. What was Sam's distance traveled? b. What was Sam's resultant displacement? c. How many yards did Sam gain in this play (how far was the ball advanced toward the goal line)?

a. 21 yd b. 15 yd c. 12 yd

direction of motion does not indicate direction of _______

accleration

A person is performing a leg press by pushing s weight up a 40 degree slope. The mass of the weight she is pushing is 120 kg. She pushes the weight 50 cm up the 40 degree slope. Show 2 ways to solve the amount of work she performed

- U=mgh.... U= (120 x 9.81 x (.5sin40))= 378 J - U=Fd....(mgsin40) x .5 = 378 J

What goes into the instruction component of qualitative biomechanical analysis(3)?

- communicate with performer (describe, demonstrate, replay) - correct error (break down skill, drills) - repeat analysis

What goes into the description component of qualitative biomechanical analysis(3)?

- fundamental knowledge of skills (rules, familiarity) - purpose or goal of skill (measure of success) - characteristic of the most effective technique (tradition vs most effective)

What are the 6 laws of rigid body mechanics?

- parallelogram law for vector addition - universal law of gravitation - Newton's 1st Law - Newton's 2nd Law - Newton's 3rd Law - Transmissibility of forces in rigid bodies

What are the 2 types of mechanical energy and give examples for both

- potential: stored energy (static); could be put into motion (gravitational, elastic) - kinetic: moving (translational, rotational)

A warm hockey puck has a coefficient of restitution of 0.50, while a frozen hockey puck has a coefficient of restitution of only 0.35. In the NHL, the pucks to be used in games are kept frozen. During a game, the referee retrieves a puck from the cooler to restart play but is told by the equipment manager that several warm pucks were just put into the cooler. To check to make sure he has a game-ready puck, the referee drops the puck on its side from a height of 2 m. How high should the puck bounce if it is a frozen puck?

0.25 m

A pitch travels 17 meters from the release by the pitcher to home plate. If the ball is moving at 95 mph horizontally how long does it take to reach home plate?

0.4 s

Jay is gliding north on his cross-country skis across a flat section of snow at 7 m/s. Jay's mass is 100 kg. The coefficient of dynamic friction between the skis and the snow is 0.10. The coefficient of static friction between the skis and the snow is 0.12. The force of air resistance is 1.9 N acting backward (south) on Jay. If friction between the skis and snow and air resistance are the only horizontal forces acting on Jay, what is his horizontal acceleration?

1 m/s ^2 backward

Quentin is lifting a 10 kg dumbbell by pulling upward on it with a 108.1 N force. What is the acceleration of the dumbbell as a result of this force?

1.0 m/s^2

The world-record times for the men's 50 m, 100 m, 200 m, and 400 m sprint races are 5.47 s, 9.58 s, 19.19 s, and 43.18 s, respectively. Which world-record race was run at the fastest average speed?

100 m at 10.44 m/s

The quadriceps pulls on the patella with a force of 1000 N while the patellar tendon pulls on the patella with a force of 1000 N also. The knee is in a flexed position, so the angle between these two forces is 120°. A compressive force from the femoral condyles is the only other significant force acting on the patella. If the patella is in static equilibrium, how large is the compressive force exerted by the femoral condyles on the patella?

1000 N force pushing anteriorly and superiorly on patella at an angle of 80.5 degrees above the horizontal

. A 0.43 kg soccer ball is stationary on the field when Darryl kicks it. Darryl's foot is in contact with the ball for 0.01 s during the kick. The horizontal velocity of the ball as it leaves his foot is 25 m/s. What is the average horizontal force exerted by Darryl's foot on the ball during the 0.01 s of contact (assume that friction between the ball and the field is zero)?

1075 N forward

During a fastball pitch, the maximum horizontal acceleration of the 146 g baseball is 1000 m/s2 What horizontal force is the pitcher exerting on the baseball at this instant to cause this acceleration?

146 N

The Achilles tendon inserts on the calcaneus (the heel bone) at a distance of 8 cm from the axis of the ankle joint. If the force generated by the muscles attached to the Achilles tendon is 3000 N, and the moment arm of this force about the ankle joint axis is 5 cm, what torque is created by these muscles about the ankle joint?

150 Nm

At the top of a giant swing on the gymnastics high bar, Candy's velocity is 1 m/s, and she is 3.5 m high. If Candy's mass is 50 kg, what is her total mechanical energy at this instant?

1742 J

When offensive lineman Aaron Gibson reported to the Buffalo Bills in 2006, he was the largest NFL player ever with a mass of 186 kg. What was Aaron's weight?

1825 N

Mike is a 70 kg pole-vaulter. He falls from a peak height of 5.90 m after pole-vaulting over a crossbar set at that height. He lands on a thick mat. When Mike first makes contact with the mat, his center of gravity is only 1.0 m high. During Mike's impact with the mat, the mat compresses. At the point of maximum compression, Mike's vertical velocity reaches zero, and his center of gravity is only 0.5 m high. What average force did the mat exert on Mike during this impact?

7416 N up150

The distance from goal line to goal line in an American football field is 100 yards. How many meters is this?

91.4 m

Compute the maximum static and kinetic frictional forces of a 60 kg sled that is pulled across a level floor if the coefficients of static and frictions are 0.95 and 0.90 respectively

Fs= 559.2 N Fd= 529.7 N

To compress a foam pit 0.1 meters requires 200 J of work. How much work is necessary to compress the same pit 0.4 meters? (Treat the pit as a spring)

U= 3200 J

Louise spikes a volleyball. At the instant the ball leaves her hand, its height is 2.6 m and its resultant velocity is 20 m/s downward and forward at an angle of 60° below horizontal. a. How long will it take for the ball to strike the floor if the opposing team does not block it? b. How far will the ball travel horizontally before it strikes the floor?

a. 0.14s b. 1.4 m

Emma is working in a shoe test lab measuring the coefficient of friction for tennis shoes on a variety of surfaces. The shoes are pushed against the surface with a force of 400 N, and a sample of the surface material is then pulled out from under the shoe by a machine. The machine pulls with a force of 300 N before the material begins to slide. When the material is sliding, the machine has to pull with a force of only 200 N to keep the material moving. a. What is the coefficient of static friction between the shoe and the material? b. What is the coefficient of dynamic friction between the shoe and the material?

a. 0.75 b. 0.50

To earn the FIFA Approved label, a soccer ball must bounce at least 135 cm high and no more than 155 cm high when dropped from a height of 200 cm onto a steel plate. a. What is the minimum coefficient of restitution of a FIFA Approved soccer ball? b. What is the maximum coefficient of restitution of a FIFA Approved soccer ball?

a. 0.82 b. 0.88

If Megan Rapinoe kicks a ball at a velocity of 18 m/s at 15 degrees above horizontal, a. What is the maximum height the ball will reach? b. How far does the ball travel before it lands on the ground?

a. 1.10 m b. 16.7 m

A FIFA-approved size 5 soccer ball must have a circumference of 68.5 to 69.5 cm and a mass of 420 to 445 grams. a. What is the circumference in inches of a FIFA-approved size 5 soccer ball? b. How much does a FIFA-approved size 5 soccer ball weigh in pounds?

a. 27 - 27.4 in b. 0.92- 0.98 lb.

Katherine is attempting a biceps curl with a 100 N dumbbell. She is standing upright, and her forearm is horizontal. The moment arm of the dumbbell about Katherine's elbow joint is 30 cm. a. What torque is created by the dumbbell about the elbow joint? b. What torque is created by Katherine's elbow flexor muscles to hold the dumbbell in this position? Ignore the weight of her arm and hand. c. If the elbow flexor muscles contract with a force of 1000 N and hold the barbell in static equilibrium, what is the moment arm of the elbow flexor muscles about the elbow joint?

a. 30 Nm b. 30 Nm c. 3 cm

What is the Law of entropy?

during any transformation of energy (from one form to another) there is always a loss of usable energy

What are the 2 types of collisions and explain each.

elastic- objects collide and rebound off of one another (separate) inelastic- collide and travel together

What does rigid body mechanics mean?

forces do not deform objects

In a vertical jump-and-reach test, 60 kg Nellie jumps 60 cm, while 90 kg Ginger jumps 45 cm. Assuming both jumps took the same amount of time, which jumper was more powerful?

ginger's jump

Use conservation of energy to determine the height from which a diver fell into the water if the speed at entry was 14 m/s.

h= 10 m

In power, force and velocity have an _______ relationship

inverse (greater the load is, cannot move it as fast)

Friction is a _____ force; it doesn't happen unless something is acting against it

reaction

T or F all velocities in projectiles are the same quantity on the way up as they are on the way down

true (mirror image) IF IT STARTS AND STOPS AT THE SAME HEIGHT

T or F you can move and be in equilibrium

true there just cannot be accleration

Doris is trying to lift a stack of books off the table. The stack of books has a mass of 15 kg. What minimum upward force must Doris exert on the books to lift the books off the table?

upward force > 147 N

Is displacement a scalar or a vector

vector; distance from start to finish

Cole is trying a biceps curl and attempting to lift a 150 N dumbbell. The moment arm of this weight about his elbow joint is 25 cm. The force created by the elbow flexor muscles is 2000 N. The moment arm of the elbow flexor muscles is 2 cm. Is Cole able to lift the weight with this amount of force in his flexor muscles?

yes, the flexor muscles create a flexor torque of 40 Nm which is sufficient to overcome the extensor torque of 37.5 created by the weight

What are the 4 components of qualitative biomechanical analysis to improve technique

- description - observation - evaluation - inspection

What goes into the evaluation component of qualitative biomechanical analysis(3)?

- identify errors (compare ideal performance to actual performance, decide whether difference are important or not i.e. strength, anthropometry) - evaluate errors - decide how to correct errors and in what order 1. major to minor 2. earliest to latest 3. easiest to most difficult

What are the 3 factors that affect stability?

- mass (weight) - base of support - height of COM

What is positive work?

- motion and force in the same direction - force doing work on a body (like lifting up a weight, or throwing a ball)

What are the 3 basic dimensions of biomechanics?

- space (length) - mass - time

It is the final seconds of an ice hockey game between the Flyers and the Bruins. The Bruins are down by 1 point. With 20 s left in the game, the Bruins pull the goalie and have him play as a forward in an attempt to tie the game. The Flyers successfully defend their goal for 9 s. With only 1.25 s remaining on the game clock, a Flyer shoots the puck on the ice past the skates and sticks of the other players and toward the Bruins' goal. The puck is 37 m from the goal when it leaves the stick with an initial horizontal velocity of 30 m/s. The shot is perfectly directed toward the empty goal, but the ice slows the puck down at a constant rate of 0.50 m/s2 as it slides toward the goal. None of the Bruins can stop the puck before it reaches the goal. a. Where is the puck when the game clock reaches zero and the horn sounds to end the game? b. Do the Flyers win the game by 1 or 2 points?

0.11 m past goal line; flyers win game by 2 points

The horizontal velocity of Bruce's fastball pitch is 40 m/s at the instant it's released from his hand. If the horizontal distance from Bruce's hand to home plate is 17.5 m at the instant of release, how much time does the batter have to react to the pitch and swing the bat?

0.44 s

Matt is sailboarding northeast across the river with a velocity of 10 m/s relative to the water. The river current is moving the water north at a velocity of 3 m/s downstream. If the angle between the relative velocity of the sailboard and the river current is 30°, what is the resultant or true velocity of the sailboard?

12.7 m/s in 23 degree east of north or 11.7 m/s north and 5 m/s east

The sprinter from problem 9 is now out of the blocks and running. If the coefficient of static friction between the track shoe and the track is 0.80, and the sprinter exerts a vertical force of 2000 N downward on the track, what is the maximum horizontal force he can generate under his shoe?

1600 N

How much longer is a 25 m pool than a 25 yd pool?

2.3 yd longer or 2.1 m longer

Mary is trying to stop a 5 kg bowling ball that is rolling toward her. Its horizontal velocity is 8.0 m/s when she begins to stop it. It takes her 2.0 s to stop the ball. What average force did Mary exert on the ball during this 2.0 s to stop it?

20 N in opposite direction of ball's velocity

The largest athlete at the 2012 London Olympics was judo athlete Ricardo Blas Jr. from Guam. He weighed 480.5 pounds. What was his mass in kilograms?

218 kg

How much does a 100 kg mass weigh in pounds?

220 lb.

Jon snatched 100 kg. In a snatch, the barbell is moved from a stationary position on the floor to a stationary position over the athlete's head. Only 0.50 s elapsed from the first movement of the barbell until it was overhead, and the barbell moved through a vertical displacement of 2.0 m. What was the Jon's average power output during the lift?

3924 W

Zoe is pole-vaulting. At the end of her approach run, she has a horizontal velocity of 8 m/s and her center of gravity is 1.0 m high. If Zoe's mass is 50 kg, estimate how high she should be able to vault if her kinetic and potential energies are all converted to potential energy.

4.26 m

Scott is rolling down a 30° slope on his skateboard. The total mass of Scott and the skateboard is 75 kg. The rolling friction between the skateboard wheels and the concrete is 9 N acting backward against the skateboard. The drag force due to air resistance is 11 N acting backward against Scott. What is Scott's acceleration?

4.64 m/s ^2 down the 30 degree slope

How much kinetic energy does a 2 kg discus have if its velocity is 20 m/s?

400 J

A marathon is 26 miles 385 yd. How many kilometers is this?

42.2 km

The coefficient of static friction between Jimmy's hand and his tennis racket is 0.45. How hard must he squeeze the racket (what is R?) if he wants to exert a total force of 200 N along the longitudinal axis of the racket?

444 N or 222 N from force of fingers and 222 N force from palm of hand

At the 2008 Beijing Olympics, Matthias Steiner of Germany won the gold medal in weightlifting in the unlimited weight class (>105 kg). He lifted 203 kg in the snatch and 258 kg in the clean and jerk for a total of 461 kg. How much does 461 kg weigh?

4522 N

Mike clears a crossbar while pole vaulting. He releases the pole before he achieves his peak height. It takes him 1 s to fall from his peak height to the landing pit. The landing pit is 1 m high. How high above the ground was Mike at the peak height of his vault?

5.91 m

How much energy is there in a 70 kg sprinter who has a linear velocity of 12.0 m/s whose center of mass is 115 cm high?

5829.7 J

How many centimeters in 1 yd?

91.4 cm

The coefficient of static friction between the sole of Ken's shoes and the basketball court floor is 0.67. If Ken exerts a normal contact force of 1400 N when he pushes off the floor to run down the court, how large is the friction force exerted by Ken's shoes on the floor?

938 N

Brian is trying to pull Julie on a sled across a flat, snowy field. Brian pulls on a rope attached to the sled. His pulling force is directed forward and upward at an angle of 30° above horizontal. Julie's mass is 50 kg, and the sled's mass is 8 kg. If the coefficient of static friction between the sled runners and the snow is 0.10, how much force must Brian exert on the rope to start moving the sled?

> 62 N

Sean is running a 100 m dash. When the starter's pistol fires, he leaves the starting block and continues speeding up until 6 s into the race, when he reaches his top speed of 11 m/s. He holds this speed for 2 s; then his speed has slowed to 10 m/s by the time he crosses the finish line 11 s after he started the race. a. What was Sean's average acceleration during the first 6 s of the race? b. What was Sean's average acceleration from 6 to 8 s into the race? c. What was Sean's average velocity for the whole race? d. What was Sean's average acceleration from 8 to 11 s into the race?

a. 1.83 m/s^2 toward finish line b. zero- his velocity did not change c. 9.09 m/s toward finish line d. 0.33 m/s^2 toward starting line

Tonya crashes into Nancy while they are practicing their figure skating routines. Tonya's mass is 60 kg and Nancy's mass is 50 kg. Just before the collision occurs, Tonya's velocity is 5 m/s and Nancy's velocity is 6 m/s in the opposite direction. During the collision, Tonya exerts an average force of 1000 N against Nancy. a. How big is the average force Nancy exerts against Tonya during the collision? b. If this is the only horizontal force acting on each skater during the collision, what average horizontal acceleration does each skater experience during the collision? c. If the collision is perfectly inelastic, how fast and in what direction will Tonya and Nancy be moving immediately after the collision?

a. 1000 N in opposite direction of the force Tonya exerts on Nancy b. Tanya will accelerate 16.67 m/s^2 in the direction of the 1000 N force that Nancy exerts on her. Nancy will accelerate 20 m/s^2 in the opposite direction c. 0m/s

Grant accelerates a 1 kg ball 5.0 m/s2 horizontally. The vertical acceleration of the ball is zero. The force of gravity is the only external force acting on the ball other than the forces Grant exerts on it. a. How large is the horizontal force Grant exerts on the ball at this instant to cause its 5.0 m/s2 horizontal acceleration? b. How large is the vertical force Grant exerts on the ball at this instant?

a. 5 N horizontal force in same direction as acceleration b. 9.81 N up

A baseball strikes the catcher's glove with a horizontal velocity of 40 m/s. The mass of the baseball is 0.15 kg. The displacement of the baseball due to the deformation of the catcher's glove and the movement of the catcher's hand is 8 cm from the instant it first makes contact with the glove until it stops. a. How much kinetic energy does the baseball possess just before it strikes the glove? b. How much work does the catcher do on the baseball during the catch? c. Is the work done positive or negative? d. What is the average impact force exerted by the glove on the baseball?

a. 120 J b. - 120 J c. negative d. 1500 N in opposite direction of ball's motion

During the pitching motion, a baseball pitcher exerted an average horizontal force of 60 N against the 0.15 kg baseball while moving it through a horizontal displacement of 2.0 m before he released it. a. How much work did the pitcher do to the baseball as a result of this force? b. Was the work done positive or negative? c. If the baseball's velocity at the start of the pitching action was zero, how fast was the ball moving at the instant of release?

a. 120 J b. positive c. 40 m/s horizontally in direction of the force

A gymnast falls from the high bar and lands on a 10 cm thick gymnastics mat. The gymnast strikes the back of his head against the mat during his landing. His head is moving at 7 m/s when it first strikes the mat. The mass of his head is 5 kg. The impact ends when the gymnast's head comes to a stop after deflecting the mat 6.5 cm. a. How much kinetic energy does the gymnast's head have at the instant just before it contacts the mat? b. How much work does the mat do to stop the motion of the gymnast's head? c. What average impact force does the mat exert on the gymnast's head during the impact? d. Estimate the peak impact force exerted by the mat on the gymnast's head. e. Estimate the peak acceleration of the gymnast's head. f. Express this peak acceleration in g's

a. 122.5 J b. -125.7 J c. 1934 N up d. 3868 N up e. 764 m/s ^2 up f. 78 g

Oliver punts a football into the air. The football has an initial vertical velocity of 15 m/s and an initial horizontal velocity of 15 m/s when it leaves the Oliver's foot. The ball experiences a constant vertical acceleration of 9.81 m/s2 downward while it is in the air. a. What is the ball's horizontal velocity 2 s after it leaves the kicker's foot? b. What is the ball's vertical velocity 2 s after it leaves the kicker's foot? c. What is the ball's horizontal displacement 2 s after it leaves the kicker's foot? d. What is the ball's vertical displacement 2 s after it leaves the kicker's foot?

a. 15 m/s forward b. 4.62 m/s downward c. 30 m forward d. 10.38 m upward

To test the impact performance of a 10 cm thick gymnastics mat, a 20 kg cylindrical mass is dropped onto the mat from a height of 1 m above the mat. During the impact, the cylinder's vertical velocity reaches zero at the instant the mat has compressed to only 4 cm thick. a. How much kinetic energy does the cylinder have at the instant just before it contacts the mat? b. How much work does the mat do to stop the fall of the cylinder? c. What average vertical force does the mat exert on the cylinder during the impact, from contact until the cylinder's vertical velocity is zero?

a. 196.2 J b. -208 J c. 3467 N up

Maddie is standing still when her dancing partner, Paul, begins to lift her up and throw her into the air. Maddie's mass is 40 kg. Paul exerts an average vertical force of 500 N for 1.0 s on Maddie during the lift and throwing motion. a. What is Maddie's vertical velocity when Paul releases her? b. If Maddie's center of gravity was 1.5 m above the floor when Paul released her, what peak height will she reach?

a. 2.70 m/s up b. 1.87 m high

Chloe has a vertical velocity of 3 m/s when she leaves the 1 m diving board. At this instant, her center of gravity is 2.5 m above the water. a. How high will Chloe go? b. How long will Chloe be in the air before she touches the water? Assume that she first touches the water when her center of gravity is 1 m above the water

a. 2.96 m b. 0.94 s

At the Dallas Cowboys Stadium, the minimum clearance height between the football field and the gigantic video screens that hang over the field is only 90 ft (27.43 m). In the first game played at the Cowboys Stadium on August 21, 2009, a punter's kick hit the video screen. a. What minimum initial vertical velocity would a football need to have to hit the video screens if it were kicked from a height 1 m above the playing field surface? Assume that air resistance does not affect the flight of the football. b. If the video screens were not in the way, what would be the hang time for a football kicked 27.43 m high? Again, assume that air resistance does not affect the flight of the football and that the ball is 1 m above the playing field when it is kicked.

a. 22.77 m/s b. 4.69 s

A 60 kg gymnast holds an iron cross position on the rings. In this position, the gymnast's arms are abducted 90° and his trunk and legs are vertical. The horizontal distance from each ring to the gymnast's closest shoulder is 0.60 m. The gymnast is in static equilibrium. a. What vertical reaction force does each ring exert on each hand? b. What torque is exerted by the right ring about the right shoulder joint? c. How much torque must the right shoulder adductor muscles produce to maintain the iron cross position? d. If the moment arm of the right shoulder adductor muscles about the shoulder joint is 5 cm, how much force must these muscles produce to maintain the iron cross?

a. 294 N b. 177 Nm c. 177 Nm d. 3532 Nm

Leigh is doing a knee extension exercise using a 100 N weight strapped to her ankle 40 cm from her knee joint. She holds her leg so that the horizontal distance from her knee joint to the weight is 30 cm. a. For this position, what torque is created by the dumbbell about her knee joint axis? b. If the moment arm of the knee extensor muscles is 4 cm about the knee joint axis, what amount of force must these muscles produce to hold the leg in the position described? Ignore the weight of the leg.

a. 30 Nm b. 750 N

Three athletes are tugging on a ring. Martha pulls with a force of 150 N directly north. Evelyn pulls with a force of 100 N directly east. Sara pulls with a force of 200 N directly southwest (225° clockwise from north). 49 a. How big is the resultant of the three forces? b. What is the direction of the resultant force?

a. 42 N b. force acts in a direction 12 degrees north of west

The ground reaction force acting on Carter during his long jump is 4500 N acting forward and upward at an angle of 78° from horizontal. Carter's mass is 70 kg. Other than gravity, this is the only external force acting on Carter. a. What is the vertical component of this ground reaction force? b. What is the horizontal component of this ground reaction force? c. How big is the net force, the sum of all the external forces, acting on Carter?

a. 4402 N b. 936 N c. 3831 N

Sam fields a baseball hit to him in the left field. He then throws the ball to third to force out the base runner, Mike. Sam releases the ball 1.80 m above the ground with a vertical velocity of 8 m/s and a horizontal velocity of 25 m/s. At the instant Sam releases the ball, he is 41 m from the third baseman, Charlie, and Mike is 13 m from third base and running at 8 m/s toward third. Assume that air resistance does not affect the flight of the ball when answering the following questions. a. How high in the air does the ball go? b. How much time does it take for the ball to reach the third baseman? c. How high is the ball when it reaches the third baseman? d. If Mike maintains a constant velocity of 8 m/s toward third base, does he reach third base before the ball reaches the third baseman?

a. 5.06 m b. 1.64 s c. 1.73 m d. yes

Matt has a portable basketball goal in his driveway. He has the basket set 8 ft (2.4 m) high so he can practice dunking the ball. He slams the ball through the hoop and then hangs onto the rim. This exerts a downward force of 600 N on the front of the rim. The front of the rim is 1.1 m in front of the front edge of the portable basketball goal's base. The mass of the whole portable basketball goal is 70 kg. The center of gravity of the portable basketball goal is 1.0 m behind the front edge of its base. a. How much torque is produced around the front of the goal base by the 600 N force Matt exerts on the front of the rim? b. How much torque would be needed to tip the goal? c. What is the largest vertical force that can be exerted on the front edge of the rim before the portable basketball goal begins to tip?

a. 660 Nm tipping torque b. > 687 Nm c. 625 N

A golf club makes impact with a 0.045 kg golf ball during a drive off the tee. The loft angle of the club (the angle between the club face and vertical) is 10°. The normal contact force exerted by the club on the ball is a 7500 N force directed forward and upward 10° above horizontal. The friction force exerted by the club on the ball is 700 N directed forward and downward 80° below horizontal. a. What is the magnitude of the vector sum of the two club head forces acting on the golf ball? b. What is the direction of this resultant force?

a. 7533 N b. 5 degrees forward and upward above horizontal

Gerri leaves the long jump takeoff board with a vertical velocity of 2.8 m/s and a horizontal velocity of 7.7 m/s. a. What is Gerri's resultant velocity at takeoff? b. What is Gerri's takeoff angle—the angle of her resultant takeoff velocity with horizontal? c. What is Gerri's horizontal velocity just before she lands? d. If Gerri is in the air for 0.71 s, what is her horizontal displacement during this time in the air? e. What is Gerri's vertical velocity at the end of her 0.71 s flight? f. If Gerri's center of gravity was 1.0 m high at the instant of takeoff, how high will it be at the peak of her flight? g. How high is Gerri's center of gravity at the end of her flight, when she first hits the pit?

a. 8.19 m/s b. 20 degrees c. 7.7 m/s d. 5.47 m e. 4.17 m/s downward f. 1.40 m g. 0.52 m

An archer draws his compound bow and shoots an arrow. The 23 g arrow leaves the bow with a velocity of 88 m/s. The power stroke of the bow is 57 cm; that is, the bowstring exerts force on the arrow through a displacement of 57 cm. The peak draw weight of the bow is 312 N. (This is the maximum force that the archer has to exert on the bowstring.) a. How much kinetic energy does the arrow have after release? b. How much work does the bowstring do on the arrow? c. What average force does the bowstring exert on the arrow?

a. 89 J b. 89 J c. 156 N

Blanche, a 100 kg shot-putter, is putting the 4 kg shot in a track meet. Just before she releases the shot, Blanche is in the air (her feet are off the ground). At this instant, the only force she exerts against the shot is an 800 N horizontal force directed forward. a. What is Blanche's horizontal acceleration at this instant? b. What is Blanche's vertical acceleration at this instant? c. What is the shot's horizontal acceleration at this instant? d. What is the shot's vertical acceleration at this instant?

a. 8m/s ^2 backward b. 9.81 m/s ^2 downward c. 200 m/s ^2 forward d. 9.81 m/s ^2 downward

Peter, a 100 kg basketball player, lands on his feet after completing a slam dunk and then immediately jumps up again to celebrate his basket. When his feet first touch the floor after the dunk, his velocity is 5 m/s downward; when his feet leave the floor 0.50 s later, as he jumps back up, his velocity is 4 m/s upward. a. What is the impulse exerted on Peter during this 0.50 s? b. What is the average net force exerted on Peter during this 0.50 s? c. What is the average reaction force exerted upward by the floor on Peter during this 0.50 s?

a. 900 Ns b. 1800 N up c. 2781 N up

You are slowly forcing your opponent's wrist to the table in an arm-wrestling match. a. Are you doing any mechanical work against your opponent? If so, is the work positive or negative? b. What type of contractions do your arm and shoulder muscles produce? c. Is your opponent doing any work against you? If so, is the work positive or negative? d. What type of contractions do your opponent's arm and shoulder muscles produce?

a. yes, positive b. concentric c. yes, your opponent is doing negative work d. eccentric

What is qualitative biomechanical analysis

breaking down a movement or sport skill into its basic elements and qualitatively examining these elements

What is translational motion and what are 2 types?

particles follow parallel path - rectilinear(straight line) - curvilinear (not straight line)

the human body was built for strength or speed

speed

A pole-vaulter is holding a vaulting pole parallel to the ground. The pole is 5 m long. The vaulter grips the pole with his right hand 10 cm from the top end of the pole and with his left hand 1 m from the top end of the pole. Although the pole is quite light (its mass is only 2.5 kg), the forces that the vaulter must exert on the pole to maintain it in this position are quite large. How large are they? (Assume that the vaulter exerts only vertical—up or down—forces on the horizontal pole and that the center of gravity of the pole is located at the center of its length.)

the right hand exerts a 40.9 N force down on the pole and the left hand exerts a 65.4 N upward force on the pole

kinetic energy is dependent on _____

velocity

When is power more important than force?

when speed is involved

When is force more important than power?

when strength is involved