biomechanics midterm

Brian is attempting to high jump over a crossbar set at 2.13 m (7.0 ft). At the instant of takeoff (when he is no longer in contact with the ground), his vertical velocity is 4.2 m/s and his center of gravity is 1.25 m high. What is Brian's vertical acceleration at the instant of takeoff? 0 m/s/s -9.8 m/s/s There is not enough information to determine the acceleration. Between 0 and 9.8 m/s/s

-9.8 m/s/s

steps to find friction on slope

1. given vertical force solve for normal force using the formula Normal force= vertical force x cos (angle of slope) 2. plug that normal force into F=uN

The world record times for the men's 60 m, 100 m, 200 m, and 400 m sprints in 2016 were 6.39 s, 9.58 s, 19.19 s, and 43.03 s respectively. Which world record race was run at the fastest average speed? (Make sure you put the fastest speed, not the slowest) 60 m 100 m 200 m 400 m

100 m

Which of newtons laws of motion is closely related to linear momentum?

1st law of motion.

Sam runs the football 30 yd before he is tackled. The straight-line distance from where he began the run to where he was tackled is 20 yd. This line makes an angle of 25 deg with the right sideline. What was Sam's resultant displacement? Less than 20 yd 20 yd 30 yd More than 30 yd

20 yd

Which of Newton's Laws of motion tells that the acceleration of an object is proportional to the force impressed? 1st 2nd 3rd 4th

2nd

Friction

A force that opposes motion between two surfaces that are in contact

Why is a negative angle of attack undesirable? Lift force increases with a negative angle of attack. A negative angle of attack increases drag force. The javelin cannot have a negative angle of attack. A negative angle of attack will decrease flight time.

A negative angle of attack will decrease flight time.

In the strain energy equation, what does 'k' represent? A: Stiffness in N/m B: Stiffness in Nm C: Energy in J D: Work in J

A: Stiffness in N/m

What are possible reasons given in the video that the runners may not match the average numbers? Leg length Body weight Foot strike pattern Maximum power All of the above All but one of the above

All of the above

What are possible sources of error in our experiment? Electrical noise and vibrations of the treadmill Inconsistency of steps Determination of the correct frames when measuring stride time All of the above Only B and C

All of the above

projectile :

An object that has been set on its path by some force and only has gravity and potentially air resistance acting on it. continues on a path due to its own inertia.

General Motion:

Any combination of at least two of the above types of motion.

Impulse

Average net force applied over a period of time. (F^T). it is the product of force and the amount of time that the force is applied.

Emily (55 kg) is standing still when her dancing partner, Ryan, begins to lift her up and throw her into the air. The resultant vertical force exerted on Emily is 130 N for 0.9 s during the lift and throwing motion. If Emily's center of gravity was 1.4 m above the floor when Ryan released her, what height above ground level will her center of gravity reach? Lower than 1.0 m Between 1.0 and 1.5 m Between 1.5 and 2.0 m Higher than 2.0 m

Between 1.5 and 2.0 m

A shot put is released at 12.7 m/s at an angle of 40 degrees. If it is released at a height of 1.6 m above ground level and lands on the ground, what will the flight time of the ball be? Ignore the effects of air resistance and use g=-9.8 m/s/s. Less than 1.8 s Between 1.8 and 2.0 s Between 2.0 and 2.2 s More than 2.2 s

Between 1.8 and 2.0 s

Jenna is standing still when her dancing partner, Tyrel, begins to lift her up and throw her into the air. Jenna's mass is 40 kg. Tyrel exerts an average vertical force of 500 N for 0.8 s on Jenna during the lift and throwing motion. What is Jenna's vertical velocity when Tyrel releases her? Use g = -9.8 m/s2. Less than 2.0 m/s Between 2.0 and 2.5 m/s Between 2.5 and 3.0 m/s More than 3.0 m/s

Between 2.0 and 2.5 m/s

Morgan is attempting to high jump over a crossbar set at 2.29 m (7 ft 6 in). At the instant of takeoff (when he is no longer in contact with the ground), his vertical velocity is 4.4 m/s and his center of gravity is 1.31 m high. What peak height does Morgan's center of gravity achieve? Less than 2.15 m above the ground Between 2.15 and 2.25 m above the ground Between 2.25 and 2.35 m above the ground More than 2.35 m above the ground

Between 2.25 and 2.35 m above the ground

The coefficient of static friction between Tammy's hand and her tennis racquet is 0.55. What is the minimum amount of force she must squeeze with to exert a force of 130 N along the longitudinal axis of the racquet? Less than 100 N Between 100 N and 200 N Between 200 N and 300 N More than 300 N

Between 200 N and 300 N

The ground reaction force acting on a long jumper is 5400 N acting forward and upward at an angle of 67 deg from horizontal. What is the horizontal component of this ground reaction force? Less than 1000 N Between 1000 N and 2000 N Between 2000 N and 3000 N Between 3000 N and 4000 N More than 4000 N

Between 2000 N and 3000 N

A gymnast's mass is 50 kg. She lands from a jump. Her initial vertical velocity when her feet first touch the ground is 4 m/s downward. What is the average resultant force exerted on her during this landing if she comes to a stop in 0.50 s? Less than 300 N Between 300 and 500 N Between 500 and 700 N More than 700 N

Between 300 and 500 N

A 57-kg runner exerts 170 N of horizontal force as she contacts the ground. The vertical ground reaction force at this time is 1050 N. 90 N of air resistance are working against her motion. What is the direction of the resultant external force relative to the ground? Between 0 and 25 deg Between 25 and 45 deg Between 45 and 65 deg Between 65 and 85 deg

Between 45 and 65 deg

. A sprinter is 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 540 N and down (vertically) against the ground with a force of 690 N. What is the direction of the resultant force relative to the ground? Less than 50 deg Between 50 and 55 deg Between 55 and 60 deg Greater than 60 deg

Between 50 and 55 deg

A cheerleader does a handstand on another cheerleader's hands. If the lower cheerleader weights 175 lb and the vertical ground reaction force is 1311 N, what must the top cheerleader's mass be to have equilibrium? Less than 40 kg Between 40 and 50 kg Between 50 and 60 kg More than 60 kg

Between 50 and 60 kg

Allison Felix (weight = 125lb) runs 23 mph in a straight line. What is her momentum? Less than 300 kgm/s Between 300 and 400 kgm/s Between 400 and 500 kgm/s Between 500 and 600 kgm/s More than 600 kgm/s

Between 500 and 600 kgm/s

In the book for this chapter, what magnitude of peak force can some elite sprinters produce? Less than 5 times body weight Between 5 and 7 times body weight Between 7 and 9 times body weight Greater than 9 times body weight

Between 7 and 9 times body weight

A 75-kg skier glides down a 20 deg slope. There is a frictional force of 105 N and air resistance of 75 N. What is the resultant force working on the skier? Between 50 and 60 N in the direction of motion Between 60 and 70 N in the direction of motion Between 70 and 80 N in the direction of motion Between 80 and 90 N in the direction of motion

Between 70 and 80 N in the direction of motion

A sprinter is 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 540 N and down (vertically) against the ground with a force of 690 N. What is the magnitude of the resultant force? Less than 800 N Between 800 N and 900 N Between 900 N and 1000 N More than 1000 N

Between 800N and 900 N

Total mechanical energy is conserved in which activity (ignore air resistance)? A: Trampoling while in contact with the trampoline B: A giant swing in gymnastics C: A dismount from the bar in gymnastics while in the air D: A pullup

C: A dismount from the bar in gymnastics while in the air

When release velocity is doubled with a release height of zero and a release angle of 45 deg, what will happen to the horizotnal displacement? A: It will double B: It will triple C: It will quadruple D: More information is needed

C: It will quadruple

A projectile leaves from above the ground and lands on the ground. Assuming an equal magnitude of velocity, what will to optimal release angle be for maximum horizontal displacement (ignore air resistance)? A: 45 degrees B: Greater than 45 degrees C: Less than 45 degrees D: All angles are equal if the velocity is the same

C: Less than 45 degrees

A ball is dropped vertically from a height of 2.1 m and rebounds to a height of 1.3 m. What is the coefficient of restitution for the ball with that surface?

Coef of Restitution: 0.79

A pinewood derby car starts down a constant slope with a constant acceleration of 2.5 m/s2. What will be its displacement after 1.2 s?

Displacement (m): 1.8

A football player runs along a curved path for 20 yd. The straight line from the start to finish of the run is 10 yd at an angle of 30 deg to the sideline. What is the distance, displacement, and yards gained (downfield component)?

Distance (yd): 20 Displacement (yd): 10 Yards Gained (yd): 8.7

Universal Law of Gravitation

Every point of mass in the universe attracts every other point of mass with a force directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers.

what should you remember about the impulse momentum equation?

F is the averag external resultant force.

F=uN units?

F=n, u=no units, N=normal force in N

At the time a basketball player makes a move, the vertical ground reaction force is 600 N. What is the maximum amount of friction that could occur before he would slip? What will the friction be after he begins to slip? The coefficient of static friction is 0.65. The coefficient of dynamic friction is 0.61.

Force before slipping (N): 390 Slipping force (N): 366

According to the lesson, how much force is required to increase bone mineral density significantly? Any force is sufficient Forces above 2 times body weight Forces greater than 1 multiple of body weight Forces must be larger than 4 times body weight

Forces above 2 times body weight

A 131 lb gymnast performs a giant swing. At one point, he is 4.8 m above the ground moving 4.2 m/s. His body is stretched 15 cm with an average stiffness of 34 kN/m. What is the total mechanical energy at this point?

GPE (J): 2801 KE (J): 525 SE (J): 383 Total Energy (J): 3709

How large was the peak force in landing from a jump in the video you watched? Less than 1000 N Between 1000 N and 2000 N Between 2000 N and 3000 N Between 3000 N and 4000 N Greater than 4000 N

Greater than 4000 N

You are trying to lift a 50 kg barbell off the ground. What is the minimum amount of upward force you must generate to lift the barbell? Less than 490 N Less than 223 N Any upwards force Greater than 490 N

Greater than 490 N

What is true about the time in contact with the ground at each pace? Ground times were all between 1 and 3 seconds. Ground time decreased exponentially as pace increased. Ground time increased exponentially as pace increased. Ground time decreased nearly linearly as pace increased.

Ground time decreased nearly linearly as pace increased.

what equation do you use to determine horizontal displacement?

HD= (FT)(Vh) no acceleration componet since gravity only works vertically

A shot put is released with a velocity of 12.5 m/s at an angle of 39 deg. What will the horizontal and vertical components be?

Horizontal (m/s): 9.7 Vertical (m/s): 7.9

During a long jump takeoff, someone pushes with 3500 N at an angle of 40 °. What are the vertical and horizontal components of this force?

Horz Force (N): 2681 Vert Force (N): 2250

Which situation will always increase running speed? Increase stride rate while decreasing stride length Decrease stride rate while increasing stride length Increase stride rate and stride length Decrease stride rate and stride length

Increase stride rate and stride length

Based off of the spreadsheet, what does our data set show about the magnitude of release velocity in javelin throwing? Velocity has no impact on distance. Velocity is by far the main factor in determining release velocity. Increasing velocity is one primary factor for improving throwing distance. Increasing velocity decreases the throwing distance.

Increasing velocity is one primary factor for improving throwing distance.

During the flight of a shot put, the vertical acceleration... Is equal to 0 m/s/s. Is a constant -9.8 m/s/s. Increases then decreases. Is positive on the way up and negative on the way down.

Is a constant -9.8 m/s/s.

On average, what is the typical trend for stride rate as running speed is increased? It increases linearly. It decreases linearly. It increases more going from slow to medium than medium to fast. It increases more going from medium to fast than slow to medium. None of the above trend

It increases more going from medium to fast than slow to medium.

On average, what is the typical trend for stride length as running speed is increased? It increases linearly. It increases more going from slow to medium speeds than medium to fast. It increases more going from medium to fast speeds than slow to medium. None of the above trends

It increases more going from slow to medium speeds than medium to fast

Why is velocity being based on displacement useful? when is it not?

It is useful because displacement is a vector quantity so you get information on direction. It would not be useful at the London marathon where the displacement is 6.3 miles, this information does not help determine speed or pace.

unit for mechanical work?

Joule!! =Nm

Newton's first law of motion

Law of inertia - body at rest stays at rest unless acted upon by an outside force. Velocity is constant when force is 0.

If a penny (2.5 g) is moving at 1.4 m/s and collides with a nickel (5.0 g), how fast will the nickel be moving after the collision if the penny comes to a stop? Less than 1.0 m/s Between 1.0 and 1.5 m/s Between 1.5 and 2.0 m/s More than 2.0 m/s

Less than 1.0 m/s

Sam runs the football 30 yd before he is tackled. The straight-line distance from where he began the run to where he was tackled is 20 yd. This line makes an angle of 25 deg with the right sideline. How many yards did Sam gain in this play? Less than 20 yd 20 yd 30 yd More than 30 yd

Less than 20 yd

A 55-kg ice skater is gliding across the ice. The coefficient of dynamic friction is 0.07. Ignoring the effect of air resistance, what will the frictional force on the skater be? Remember: weight in kg times gravitational force equals the normal force in Newtons. Less than 50 N Between 50 N and 60 N Between 60 N and 70 N More than 70 N

Less than 50 N

During a sprint start, someone pushes with 1200N of horizontal force and 1600 N of vertical force. What is the resultant of this push?

Magnitude (N): 2000 Direction (deg): 53

A shot put is released with a velocity of 12.5 m/s at an angle of 39 deg and a height of 2.2 m. How high will it get? How long will it be in the air? What will be the horizontal displacement?

Maximum Height (m): 5.4 Flight Time (s): 1.85 Horizontal Displacement (m): 17.96

When does maximum height occur?

Maximum Height: Maximum height occurs when a projectile is halfway through the flight time from take-off until it returns to the height it left from.

What was the main method we used for minimizing errors in our measurements? Changing the settings of the treadmill force plates Measuring 20 steps and averaging Telling the subject to run with consistent steps Decreasing the vibrations of the treadmill

Measuring 20 steps and averaging

What do our graphs imply about the best throwers in the competition? More successful throwers have a relatively high angle of attack and a high release velocity. If throwers could determine a way to increase angle of attack above 20, they would have a greater release velocity To increase release velocity beyond 29 m/s, throwers would have an angle of attack greater than 20 deg. Angle of attack was not correlated with release velocity.

More successful throwers have a relatively high angle of attack and a high release velocity.

A runner increases his pace to pass someone. He goes from 6.5 m/s to 6.8 m/s in 0.57 s. What is his acceleration? Less than -0.5 m/s/s Between 0 and -0.5 m/s/s There is no acceleration Between 0 and 0.5 m/s/s More than 0.5 m/s/s

More than 0.5 m/s/s

The ground reaction force acting on a long jumper is 5400 N acting forward and upward at an angle of 67 deg from horizontal. What is the vertical component of this ground reaction force? Less than 1000 N 1000 N and 2000 N Between 2000 N and 3000 N Between 3000 N and 4000 N More than 4000 N

More than 4000 N

Curvilinear translation:

Motion along a curved path with no change in orientation.

Rectilinear translation:

Motion in a straight line with no change in orientation.

What is the optimal angle of attack according to our discussion? It should be minimized. Release angle as half the pitch angle Near 15 degrees It should be maximized.

Near 15 degrees

A 65 -kg skier is gliding down a 20 -deg slope. What will the normal force be? What will the downhill component of gravity be?

Normal Force (N): 599 Downhill Component of Gravity (N): 218

Which combination is desirable for increasing throwing distance? Optimizing angle of attack through increasing pitch angle. Choose an angle of attack close to zero. Optimize angle of attack through decreasing release angle. Create the largest possible angle of attack.

Optimizing angle of attack through increasing pitch angle.

A 189 lb hockey player is skating at 7.2m/s. Does a 157 -lb player moving 8.1 m/s in the opposite direction have enough momentum to stop him?

Player 1 (kg m/s): 618.5 Player 2 (kg m/s): 578 Enough Momentum: No

someone performs a standing vertical jump starting from a squatted position. If an average vertical force of 350 is applied for 0.4 s while he goes through a displacement of 0.6 m, what is the average power during this push off the ground?

Power (W): 525

Forces in walking reach magnitudes of Less than body weight Relatively close to body weight Much larger than body weight Similar to running

Relatively close to body weight

Inertia

Resistance of an object to a change in its motion

rolling friction - formula and units

Rolling friction (F) equals the product of a coefficient of friction (μ) and weight (W) divided by radius of a cylinder (r). F=u(W/r)

angular motion

Rotation of all points on an object around an axis.

Distance vs Displacement, which is useful in swimming and which is useful in marathons and why

Running a marathon is an example where distance is a useful measure. The distance is always 26 miles 385 yards no matter what the displacement is. However, a 50-m swimmer would need to complete 50 meters of displacement even if he does not go in exactly a straight line

Someone with a midfoot rather than a heel strike tends to have: Shorter strides Longer strides More time in contact with the ground during each step A larger peak force

Shorter strides

coefficient of restitution - what formulas to use.

Simple formula based on bounce and drop heights is used when initial velocity is 0.

Unusual examples of equilibrium- weightlifting and gliding skater. explain

Some other examples of constant motion when the resultant force is zero include: A gliding skater or hockey puck (very small amounts of friction) Lifting a dumbell at a constant velocity (here the lifting force equals the force of gravity providing a resultant force of zero).

Usain Bolt runs 19.19 s for 200m. What is his average speed for the race in m/s and miles per hour?

Speed (m/s):10.42 Speed (mph): 23.31

The mass of an astronaut is 84 kg on the surface of the earth. What will be his mass in outer space? Zero Still 84 kg 823 N -823 N

Still 84 kg

Which is a valid calculation for running speed? Stride length multiplied by stride rate Stride length divided by stride rate Stride length multiplied by stride time Stride time divided by stride length

Stride length multiplied by stride rate

A 165-lb student lands from a vertical jump and immediately jumps vertically again. The average ground reaction force is 1735 N which is applied for 0.33 s. He was moving 1.2 m/s downwards when he first contacted the ground. What will his velocity be at takeoff? What will be his jump height?

Takeoff Vel (m/s):3.2 Jump Height (m):0.5

Why is the optimal release angle not 45 degrees for the javelin? If the angle of attack was high enough, 45 degrees would be optimal The air creates a greater flight time if the javelin is thrown well, so such a steep angle is not needed. A better throw would have a release angle of 45 degrees An negative angle of attack would lead to an optimal angle of 45 degrees

The air creates a greater flight time if the javelin is thrown well, so such a steep angle is not needed.

strain potential energy :

The energy an object possesses due to its stiffness and deformation. Strain potential energy is measured in Joules.

According to the lesson, what else is required in exercise used to increase bone mineral density? The force must be applied rapidly. The force must be maintained for many seconds. The force must be applied from multiple directions. The force should have a very slow buildup.

The force must be applied rapidly.

In looking at the graphs of different running speeds, what happens to the rise rate (buildup of force across time) as pace increases? The higher the pace, the gentler the rise rate The rise rate was exactly the same across speeds The higher the pace, the steeper the rise rate

The higher the pace, the steeper the rise rate

What would occur with a javelin of lower mass with exactly the same dimensions? The javelin would accelerate less. There would be no change in acceleration. There would be an small initial acceleration, but less acceleration later in the flight. The javelin would accelerate more.

The javelin would accelerate more.

why do high jumpers land on foam mats vs concrete?

To decrease the momentum of the impact by causing the impact to occur over a longer period of time as the mat deforms. They land with less force, which hurts a lot less. Same logic of increasing impact time is used when "following through" with the bat on a baseball swing to increase momentum, as the force is applied over a longer period of time.

when is an object accelerating?

When an object is speeding up, slowing down, or changing direction, it is accelerating.

What is true about how peak force was related to running pace? With every increase in pace, there was an increase with peak force. There is a perfectly linear relationship between pace and peak force. With every increase in pace, there was a decrease with peak force. Peak force did not change as pace increased.

With every increase in pace, there was an increase with peak force.

A 108 lb person does a pullup. On the way up, how much work does he do if he goes through a vertical displacement of 43cm? How much work does he do on the way down

Work on Way Up (J): 207 Work on Way Down (J): -207

Normal Force

a force that acts on a surface in a direction perpendicular to the surface. (foot on ground, hand on racket)

Mass

a measure of the inertia of an object and depends on the amount of matter the object contains

external forces

act on a system or body due to its interaction with its surroundings (gravity, air resistance, friction, collision)

Newton's Third Law of Motion

action reaction

elastic collision

all of the systems total momentum is conserved. objects bounce off of eachother.

A baseball is pitched at 42 m/s. The bat is moving 40 m/s in exactly the opposite direction to the ball immediately before the impact. After the impact, the bat is slowed to 38m/s while the ball is moving at 60 m/s in the direction the bat was swinging. What is the coefficient of restitution?

coef= .27

Linear Kinematics

description of the linear motion of a body. includes 3D of orientation and 3D of position.

football example, describe distance displacement and yards gained

distance is total path taken, displacement is straight line from start to finish, total yards gained is displacement in the downfield direction

formula for downhill acceleration due to gravity on a slope

downhill acceleration= vertical force x sin (angle of slope)

what muscle action is associated with negative mechanical work? Positve work?

eccentric(-), concentric (+)

Newton's Second Law of Motion

f=ma

True or false: A car driving around a curve at a constant speed of 32 mph is not accelerating because the speed is constant. True False

false

static friction

force acting between two surfaces that are not moving relative to each other, opposes direction of force. Example is shoe on ground while running. u is usually larger than dynamic.

formula for normal force on a slope

he general formula is: Normal Force = Vertical Force x cos (angle of the slope).

Which quantity equals a change in linear momentum? impulse impact force work

impulse

Which of the following is not a projectile? A: Paper airplane B: Shot put C: Jet plane D: Diver

jet plane

The product of a body's mass and its linear velocity defines Linear momentum Linear impulse Linear torque Linear inertia mechanical work

linear momentum

what is the universal gravitational force based on?

masses of the two objects being investigated

On a slope, is normal force equal to body weight?

naaaaaah. only on level ground

inelastic collision

none of the systems linear momentum is conserved. objects collide and stick together.

Dynamic Friction

occurs when two dry surfaces are sliding between each other. example is gliding shuffleboard puck.

mechanical work

product of force and displacement in the direction of the force. mecanical work id the ability of a force to act through a given displacement and transfer mechanical energy. U=Fd, AVERAGE force and displacement.

coefficent of restitution

ration of relative velocities before and after an impact. helps quantify elasticity of a collision. Tells that ration of kinetic energy that is preserved in a collision, as the rest of the energy is usually given off as heat in not perfectly elastic conditions. Value is based upon the properties of both colliding objects, NOT upon teh velocity of impact, so initial velocity does not matter. a single object doesn't have a coefficient of restitution.

What happens to the coefficient of restitution as speed of impact increases (through a relatively narrow range of speeds)? It also increases It decreases It stays the same

stays the same

rolling friction

the force resisting the motion when a body (such as a ball, tire, or wheel) rolls on a surface, due to the deformation of one or both objects. u depends on the properties of both objects.

Mechanical Power

the rate of doing mechanical work

The slope of a graph of position versus time will give: Position Velocity Acceleration Jerk

velocity

what is the primary determinant of a sprinters maximum speed?

vertical ground reaction force. foot spends less time on the ground and greater speeds are attained

when is frictional force generated?

when a normal force is applied between two surfaces. Will always be in existence!

what equation do you use to determine vertical position of a projectile?

y= Y. + Vyt + 1/2 gt squared