PHY 2053 Lecture Notes - Lecture 3: Friction, Pogo Stick, Auto Racing

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viridiancaribou590

3 Aug 2017

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Fne t = s qrt[(ve rtica l force )^2+(horizonta l force )^2] F = ma s s *a cce le ra tion a = 2. 10 m/s ^2. Mini exa m #2: two force s a re a pplie d to a 5. 06kg obje ct; one is 5. 84n to the +y a xis , a nd the othe r is 8. 90n to the -x a xis . Wha t is the ma gnitude of the a cce le ra tion (in m/s ^2) of the obje ct. S ta tic friction = coe fficie nt friction * force. Force = ma s s *gra vity fina l ve locity = initia l ve locity + a cc*time coe fficie nt friction = v - v0 / gt. How much work is done by a boy pulling his s is te r 33m in a wa gon.

Related Questions

1. An object of mass 19 kg is placed on incline with friction.The incline is originally horizontal and then raised slowly and at21 degrees, the mass begins to slide down the incline. It is foundthat the coefficient of kinetic friction is 0.79 times thecoefficient of static friction. If the same object (same mass) isplaced on the same incline with an inclination angle of 42.2degrees (the mass will slide down the incline at this angle), whatis the magnitude of the acceleration on the mass in m/s2?
2. A mass enters the bottom of a 50 degree incline with acoefficient of kinetic friction of 0.6. At the bottom of theincline the mass is moving at 33 m/s and is moving up the incline.After the mass has traveled, 25 meters up the incline, what is themagnitude of its velocity in m/s?
3. A car is traveling around a circular, banked track withoutfriction. It is initially traveling around the bottom of the ramp(on the ground) where the inner radius of track is 351 meters. Thecar then increases its velocity by a factor of 1.7. If theinclination angle is 10 degrees, what is the height (verticaldistance above the ground) the car is traveling at this newvelocity. Answer in meters.
4. An yo-yo with a mass of 2.4 kg is swung in a vertical circle. Itis found that the string breaks at 228 Newtons. If its the yo-yo'sspeed is a constant and is the maximum speed the yo-yo can movebefore the string breaks, what is the the tension in the string atthe top of the circle in Newtons?
5. A roller coaster cart of mass 15.8 kg travels on the inside of aroller coaster track in a loop of radius 23.1 meters. The circle isa vertical circle similar to the yo-yo example done in class. Ifthe cart travels at a constant speed around the track and the valueof this speed is the minimum speed such that cart does not fall offthe track at the top of the track, was is the magnitude of thenormal force on the cart at the bottom of the track in Newtons?

1. An object is dropped from a height.Once it is moving,which ofthe following statements are true,at least at one point?
a)its velocity is more than its accelerations
b)its velocity is less than its acceleration
c)its velocity is the same as its acceleration
d)its velocity is never equal to its acceleration

2. Which type of quantity is characterized by both magnitude anddirection?
a)scalar
b)vector
c)trigonometric
d)algebraic variable

3. A hiker walks 200m west and then walks 100m north. In whatdirection is her resulting displacement?
a)north
b)west
c)northwest
d)none of the answer is correct

4. Vector 1 is 7 units long and is at 70 degree. Vector 2 is 5units long and is at 225 degree. Vector 3 is a 3 units long and isat 150 degree. Which vector has equal magnitude components?
a)Vector 1
b)vector2
c)vector 3
d)none of the vectors has equal magnitude components??????

5. Which of the following is an example of the type of force thatacts at a distance?
a)gravitational
b)magnetic
c)electrical
d)all of the above

6. A crate weight W is being pushed across a horizontal surface bya force directed at an angle of 20 degrees below the horizontal.What is the magnitude of the normal force on the crate?
a)it is less then W
b)it equals W
c)it is more than W
d)none of the above since the coefficient of kinetic friction isnot given

7. The net force on an object is in the positive x-direction.Consider the following statements.
(i) The object can be moving in the negative x-direction.
(ii) The object can be speeding up.
(iii) The object can be slowing down.
(iv) The object can be moving in the positive y-direction.

Which of the statements are true?
a. (i) and (ii)
b. (ii) and (iii)
c. (iii) and (iv)
d. Choose this answer if all the statements are true.

8.The work done by static friction can be:
a. positive.
b. negative.
c. zero.
d. Any of the above.

9.The rate at which work is done is equivalent to which of thefollowing?
a. increase in potential energy
b. thermal energy
c. potential energy
d. power

10.The dimensional equivalent of the quantity impulse in terms ofthe fundamental quantities (mass, length,
time) is which of the following?
a. MLT-1
b. ML2T-2
c. MLT
d. MLT-2

11. The dimensional equivalence of the quantity "momentum" in termsof the fundamental quantities (mass,
length, time) is:
a. MLT-1.
b. ML2T-2.
c. MLT.
d. MLT-2.

12.In order for a satellite to be geosynchronous, its orbitmust:
a. go over the North and South Poles.
b. be over the equator.
c. be over a single longitude.
d. emit television signals.

13. The quantity "angular momentum" (in terms of the fundamentalquantities of mass, length, and time) is equivalent
to:
a. MLT-2.
b. ML2T-1.
c. ML2T-3.
d. ML3T.
d. MLT-2.

1.

While helping a friend move, you push a 11.5 kg dolly with a forceof 11.0 N. Assume there are no other forces acting on the dolly. Ifthe dolly starts at rest, how far does it move in 3.50 s?
1 m

2.

At a lumberjack competition an axe with a mass of 1.25 kg is thrownat a target with a speed of 41 m/s. When it hits the target, itpenetrates to a depth of 0.055 m.
(a) What was the average force exerted by the target on theaxe?
1 N

(b) If the mass of the axe is halved, and the force exerted by thetarget on the axe remains the same, by what multiplicative factordoes the penetration depth change?
2
It doubles. It increases by a factor of the square root of two. Itdoes not change. It decreases by a factor of the square root oftwo. It halves.
Your work in question(s) will also be submitted or saved.
3

Your 1500 kg car pulls a 540 kg trailer away from a stop sign withan acceleration of 2.00 m/s2. (Note the answers should be given inkN.)
(a) What is the net force exerted by the car on the trailer?
1 kN

(b) What force does the trailer exert on the car?
2 kN

(c) What is the net force acting on the car?
3 kN

4.

Two boxes sit next to, and touching, each other on a frictionlesshorizontal surface. The lighter box has a mass of 5.31 kg and theheavier box has a mass of 7.29 kg.
(a) Find the contact force between these boxes when a horizontalforce of 6.1 N is applied to the light one.
1 N

(b) If the 6.1 N force is applied to the heavy box instead, is thecontact force between the boxes the same as, greater than, or lessthan the contact force in part (a)?
2

(c) Verify your answer to part (b) by calculating the contact forcein this case.
3 N

5.

A child sits in a wagon and together they have a mass of 25 kg. Thewagon is pulled with a constant speed by a handle that is at anangle of 22Â° above the horizontal. If the normal force exerted onthe wagon is 210 N, what is the force F applied to thehandle?
1 N

6.

An object acted on by three forces moves with constant velocity.One force acting on the object is in the positive x direction andhas a magnitude of 6.7 N; a second force has a magnitude of 4.5 Nand points in the negative y direction. Find the direction andmagnitude of the third force acting on the object.
1 N
2Â° (counterclockwise from the +x axis)

7.

A chain is used to lift a 1200 kg car vertically upward with anacceleration of 0.90 m/s2. What is the tension in the chain?
1 N

8.

A 22.5 kg box (m1) rests on a table.

(a) What is the weight of the box?
1 N
What is the normal force acting on it?
2 N (upward)
(b) A 12.5 kg box (m2) is placed directly on top of the 22.5 kgbox.
Determine the normal force that the table exerts on the 22.5 kgbox.
3 N (upward)
Determine the normal force that the 22.5 kg box exerts on the 12.5kg box.
4 N (upward)

9.

Your friend has a weight of 127 lb when standing on a scale. Youtake the scale to an elevator where you notice your friend's weighton the scale reads 108 lb. What are the direction and magnitude ofthe elevator's acceleration?
Direction 1
Magnitude 2 m/s2

10.

When you lift a package with a force of 82 N, the packageaccelerates upward at a rate of a. If, instead, you lift with aforce of 93 N, the package now has an acceleration of 8 multipliedby a.
(a) Find the weight of the package.
1 N

(b) Find the acceleration a.
2 m/s2

11.

One 3.1 kg paint bucket is hanging by a massless cord from another3.1 kg paint bucket, also hanging by a massless cord, as shownbelow.

(a) If the buckets are at rest, what is the tension in eachcord?
(lower cord) 1 N
(upper cord) 2 N

(b) If the two buckets are pulled upward with an acceleration of1.30 m/s2 by the upper cord, calculate the tension in eachcord.
(lower cord) 3 N
(upper cord)5

12)
Your friend has a pair of fuzzy dice with a mass of 1.32 g hangingfrom his rear-view mirror.
(a) When he accelerates from a stoplight, the dice deflect backwardtoward the rear of the car hanging at an angle of 6.18Â° relative tothe vertical. Find the tension in the string holding thedice.
N

(b) At what angle to the vertical will the tension in the string betwice the weight of the dice?
Â°

PHY 2053 Lecture Notes - Lecture 3: Friction, Pogo Stick, Auto Racing

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