University of Texas PHY 57880 Final Exam 2014

PHYS 211 – Final Exam Spring 2014 Sample 2 Solutions

1) A waiter is in an elevator, holding a stack of dishes. As observed by someone standing still on the ground floor, watching the elevator move down towards them with constantspeed, what is the sign of the work done bythe uppermost dish onthe onedirectly below it?

2) The figure below shows the relation between position x and time t for a particle. Which of the following statements are true?

1. The particle’s velocity is negative at a.

1. The particle’s acceleration is zero at a.

1. The particle’s acceleration is negative at f.

1. The particle’s velocity is negative at b.

1. The particle’s acceleration is roughly zero at c.

1. The particle’s velocity is zero at c.

1. 1, 2, 6

1. 3, 4, 5

1. 4, 6

1. 2, 3, 4

1. 2, 5

 

PHYS 211 – Final Exam Sample 2 Solutions

3) A particle is in simple harmonic motion with period T. At time t = 0 it is halfway between the equilibrium point and an end point of its motion, traveling toward the end point. The next time it is at the same place is:

A. t = T

B. t = T/2

C. t = T/4

D. t = T/8

₄₎A performer, seated on a trapeze, is swinging back and forth with a period of 8 s. If she stands up, thus raising the center of mass of the performer + trapeze system by 48 cm, what will be the new period of the trapeze? (Treat the system as a simple pendulum.)

A. 8.00 s

B. 11.5 s

C. 7.88 s

D. 5.01 s

E. 8.12 s

5) A bomber flying in level flight with constant velocity releases a bomb before it is over the target. Neglecting air resistance, which one of the following is NOT true?

A. The bomber is over the target when the bomb strikes.

B. The acceleration of the bomb is constant

C. The horizontal velocity of the plane equals the vertical velocity of the bomb when it hits the target

D. The bomb travels in a curved path.

E. The time of flight of the bomb is independent of the horizontal speed of the plane.

 

PHYS 211 – Final Exam Sample 2 Solutions

6) A man, holding a weight in each hand, stands at the center of a horizontal frictionless rotating turntable. The effect of the weights is to double the rotational inertia of the system. As he is rotating, the man opens his hands and drops the two weights. They fall outside the turntable.

Then:

1. his angular velocity doubles.

1. his angular velocity remains about the same.

1. his angular velocity is halved.

1. the direction of his angular momentum vector changes.

1. his rotational kinetic energy increases.

7) A block attached to a spring oscillates in simple harmonic motion along the x axis. The limits of its motion are x = 10 cm and x = 50 cm and it goes from one of these extremes to the other in 0.25 s. Its amplitude and frequency are:

	A. 40 cm, 2 Hz
	B. 20 cm, 4 Hz
	C. 60 cm, 2 Hz
	D. 25 cm, 4 Hz
	E. 20 cm, 2 Hz
8) A ball is released from rest on a no-slip surface,
as shown in the figure. After reaching its lowest
point, the ball begins to rise again, this time on a
frictionless surface as shown in the figure. When the
ball reaches its maximum height on the frictionless
surface, it is
	A. at a greater height as when it was released.
	B. at a lesser height as when it was released.
	C. at the same height as when it was released.
	D. It is impossible to tell without knowing the
	mass of the ball.
	E. It is impossible to tell without knowing the
	radius of the ball.

PHYS 211 – Final Exam Sample 2 Solutions

9) An object on the end of a spring is set into oscillation by giving it an initial velocity while it is at its equilibrium position. In the first trial the initial velocity vis0 and in the second it is 4v0. In the second trial:

A. the amplitude is half as great and the maximum acceleration is twice as great.

B. the amplitude is twice as great and the maximum acceleration is half as great.

C. both the amplitude and the maximum acceleration are twice as great.

D. both the amplitude and the maximum acceleration are four times as great.

E. the amplitude is four times as great and the maximum acceleration is twice as great.

10) Consider a cylindrical toy which can switch from having its mass roughly equally distributed across its cross-section (solid cylinder) to having its mass concentrated at its outer edge (hollow cylinder). With the toy spinning on frictionless bearings around its central symmetry axis, you push a button and it converts from “solid” to “hollow” mode.

What happens to its rotational kinetic energy?

1. Increases by a factor of 4

1. Increases by a factor of 2

1. Stays the same

1. Decreases by a factor of 2

1. Decreases by a factor of 4

PHYS 211 – Final Exam Sample 2 Solutions

11) Consider this mobile in static equilibrium. The mobile is made with three masses, several massless cords, and two rod of negligible mass. If the mass labeled C is M, what is the mass of B?

A. M/6

B. M/2

C. M/3

D. M

E. 4M/3

12) A simple pendulum has length L and period T. As it passes through its equilibrium position, the string is suddenly clamped at its midpoint. The period then becomes:

A. 2T

B. T

C. T/2

D. T/4

E. none of these

PHYS 211 – Final Exam Sample 2 Solutions

13) Two particles, each of mass m, are a distance d apart. To bring a third particle, with mass 2m, from far away to a resting point midway between the two particles, the work done by an external agent is given by:

A. 4Gm²/d

B. -4Gm²/d

C. 8Gm²/d

D. -8Gm²/d

E. 0

 

PHYS 211 – Final Exam Sample 2 Solutions

14) The velocity of an object is given by the expression v(t) = 3.00 m/s + (4.00 m/s³)t². Determine the position of the object as a function of time if it is located at x = 1.00 m at time t = 0.000 s.

t

A.

(4.00 m/s)t + 1.00 m

s3

B.

(3.00 m/s)t + (1.33 m/s3)t3

m

C.

(4.00 m/s)t

D. 1.33 m

E. 1.00 m + (3.00 m/s)t + (1.33 m/s³)t³

15) A 4.0 kg brick slides on a frictionless floor at 2.0 m/s in the positive y-direction. A sticky piece of putty with a mass of 1.0 kg slides at 6.0 m/s in the negative x-direction. The two collide and stick together. What is the speed of the brick-putty mass after the

 

collision?

1. 0.4 m/s

1. 2.0 m/s

1. 2.8 m/s

1. 10 m/s

1. None of the above

 

of linear momentum: (don’t forget 2Dv

=

f

f

f

s

s

 

16)Two uniform circular wire loops of radius R and mass M are attached as shown. What is the 10.Sec07/23

moment of inertia of this object around an axis perpendicular to the page and through the point

O? Note: The moment of inertia of a single ring around an axis through the center and

perpendicular to the ring is MR².

A. MR2

B. 2MR2

C. 4MR2

D. 8MR2

E. 16MR2

 

PHYS 211 – Final Exam Sample 2 Solutions

17) A pulley with radius R and moment of inertia I is free to rotate around a horizontal fixed axis through its center. A string passing over the pulley is attached to m₁ on one end and m₂ on the other. You observe m₁ is moving downward with speed v. If the string does not slip on the pulley, what is the approximate magnitude of the total angular momentum of the masses and pulley, taken around the pulley axis?

1. |(m₁ – m₂)vR + Iv/R|
2. |(m₁ + m₂)vR + Iv/R|
3. |(m₁ – m₂)vR – Iv/R|

1. |(m₁ + m₂)vR – Iv/R|

1. none of the above

18)The length of a bicycle pedal arm is 12cm, and a downward force of 170 N is applied to the 10.Sec09/10pedal by the rider’s foot. What is the magnitude of the torque about the pedal arm’s pivot point

when the arm makes a 65º angle with the vertical?

A. 20.4 Nm

B. 8.62 Nm

C. 4.20 Nm

D. 18.5 Nm

E. 5.05 Nm

 

PHYS 211 – Final Exam Sample 2 Solutions

19)The mass of planet Nittany is 3 times that of Earth and its radius is one half that of Earth. A toad13.Sec04/4 weighing 300 N on Earth will weigh how much on Nittany?

A. 3600 N

B. 1800 N

C. 400 N

D. 225 N

E. 25 N

 

20) A heavy ball of putty (mass m=0.50 kg, speed v₀=10 m/s) is thrown at a block of wood (mass M=1.0 kg) which hangs at rest from a cord. The putty sticks to the wood. In the figure, snapshots show the system just before the putty hits, and later, when the putty/block system has just come to a halt at the high point of its swing.

 

Bef ore

v0
m	M

After

h m+M

 

In the “after” picture, the center of mass of the whole system has risen a height “h”.

 

What is h? (Use g = 10 m/s²)

1. 0.56 m

1. 1.7 m
2. 2.5 m
3. 5.0 m
4. 10. m

 

9

 

PHYS 211 – Final Exam	Sample 2	Solutions
21) A hand pushes horizontally with a constant force on a physics book,
holding it up against a wall. Nothing is moving.					ms
The coefficient of static friction between the wall and book isms.		F(hand)
However, there is zero static friction between the hand and the book.

If the hand suddenly increases its horizontal push to TWICE what it was before, what happens to the frictional force of the wall on the book?

1. It doubles
2. It increases by more than a factor of 2
3. It increases, but by less than a factor of 2.
4. It decreases.

1. It stays exactly the same

22) A cart is moving with a constant horizontal velocity of 5 m/s. A small pebble (of negligible mass) is launched from the front of the cart with a velocity of103m/s at 60.0° above the horizontal as measured relative to the cart (see figure) and experiences no significant air resistance. Using the approximation that g = 10 m/s², just as the pebble returns to the level from which it was launched, its distance from the front of the cart is closest to

 

A) 15(3-1) m.

B) 15(3+1)m.

C) 103m.

D) 153m.

E) 203m.

 

103m/s

5 m/s

s2

 

PHYS 211 – Final Exam Sample 2 Solutions

23) If we neglect the Earth’s atmosphere and any rotational effects, with what initial minimum speed would we have to fire a projectile vertically in order for it never to fall back down? The Earth

has mass ME = 6×10²⁴ kg and is a sphere of radius RE = 6.4 ×10⁶ m. The projectile is an inert mass acted on by gravity alone, and is not a rocket.

A. 11,200 m/s

B. 4,400 m/s

C. 22,200 m/s

D. 67,300 m/s

E. 123,400 m/s

 

PHYS 211 – Final Exam Sample 2 Solutions

24) A mass moves on a frictionless plane. It is attached to a string (length r) and is swinging about the origin with constantly increasing angular velocity. At time t = 0 s it is

moving with velocity	ˆ	and has a linear acceleration pointing 45 degrees above the –x
vj
ˆ	ˆ
axis in the(-i	+ j)direction. From this point in time how long will you have to wait for its

speed to double?

A. rv

B. 2rv

C. 2p r v

1. It is impossible to know with the given information

1. None of the above

25) A swimmer heads directly across a river 300 m wide. A person with a radar gun stands 400 m downstream on the opposite bank and sees the swimmer heading straight at them at 1 m/s. How fast is the river flowing?

A. 1 m/s

B. 0.8 m/s		400 m
		vriver
C. 0.6 m/s	300 m
D. Not enough information to determine	vstill water	500 m
	E. None of the above	vwrt landClick here to have a similar paper done for you by one of our writers within the set deadline at a discounted…