PHY 161
if you put 50g of ice at 0c into 400 ml of hot tea at 92 temperature inside a thermally insulated container, what will be the final temperature of the mixture?
(Mi + Mt)CwTp = temp MtCw-MiLp
a block at the bottom of a frictionless inclined plane with an incline angle of 30, has been given an initial velocity of 20 m/s up the plane. a. what is the speed of the block after 2.0s? b. how far will the block slide up along the inclined plane before starting to slide back down? c. draw the acceleration vs time graph of the block.
(a) a = -gsin(theta) v = vo + a(t) (b) vtop = 0 a = -gsin(theta) v2-vo2=2a(x) x = v2-vo2/2a (c) draw line straight at acceleration (d) v(0) = one point at v and slope is acceleration.
which student has the largest power output?
(mg*x)/time
A skydiver jumps from a hovering plane. When the skydiver, of mass m, reaches their maximum speed, the drag force on the skydiver is?
=mg
a one meter board with a mass of 10 kg hangs by a rope, attached at the 20 cm mark (from left) as shown. A block is hung from the left as shown. If the board is to be balanced level to the ground, what should be the mass of the block?
?????
You are driving at 45 MPH when the light at the intersection 110 m ahead of you turns red. Assume your reaction time is 0.70s and that your car brakes at a constant acceleration. What acceleration will bring your car to rest right at the intersection?
Change Vo to m/s X is Vo (t) X= initial (m) - X found V^2 - Vo^2 = 2 (a) (x2)
in the hammer throw, an athlete spins a heavy mass in a horizontal circle before releasing it for distance. The "hammer" is a mass of 7.0kg. If the athlete swings the hammer at a speed of 29 m/s, by how much does the cable stretch?
F = mv^2/R delta L = F(L)/Ypi(D/2)^2
a person pulls a block across a rough horizontal surface at a constant speed by applying a force F. The arrows in the diagram below correctly indicate the direction but not necessarily the magnitudes of the various forces on the block. Which of the following relations among the forces magnitudes W, K (a force of kinetic friction), N and F must be true?
F > k and N < W
a 4.0 kg block has an acceleration of 0.20 m/s^2 when a force is exerted on it. What will be the acceleration of a second block of mass 2.0 kg when the same force is applied to it?
F=ma
a 200 g ball is dropped from a height of 2.0m and bounces on a hard floor. The impulsive force on the ball is given. How high does the ball rebound? J = area under the curve
J = delta p = area under the curve vf-vi = delta p/m before: vi = -square root(2gh) vf-vi = delta p/m (found first)-(-v found before) after = wtot = delta k -mgh2= 0-1/2mv^2
a mass m attached to the end of a string revolves in a circle on a frictionless tabletop. The other end of the string passes through a hole in the table. Initially the ball rotates with a speed of.. .
Li = Lf mR^2(W)=MR^2(W) MRv=MrV
three different materials of identical mass are placed one at a time in a special freezer that can extract energy from a material at a certain constant rate. During the cooling process, each material begins in the liquid state and ends in the solid state. Rank the materials according to their heat of fusion, greatest first.
Longest horizontal line = greater heat of fusion.
The figure shows 3 paths for a football kicked from the ground level. Rank the time according to the hang-time.
Vertical distances = so the hang times are =
a student on planet exidor, throws a ball and it follows the parabolic path shown in the figure. The x- and y- components of the initial velocity are shown (in m/s). What is the acceleration of gravity on planet Exidor?
Vy = Voy + ay(t)
a block with mass m is placed against a spring on a frictionless incline with angle theta. The block is pressed against the spring compressing it by 20.0cm and then released. How far will the block travel along the incline plane before it starts to come back down?
Wtot = K Wg + Ws = 0 -mgh + 1/2kx^2 = 0 mgLsintheta = 1/2kx^2 L= 1/2kx^2/(mgsintheta)
a quarter is dropped from rest from a height of 5 m. the speed of the quarter is v just before striking the ground. From what height would the quarter have to be dropped from rest for the speed just before striking the found to be approximately 2v?
Wtot= K mgh = 1/2mv^2 25m
Bars A and B are attached to a wall on the left and pulled with equal forces to the right. Bar B, with twice the radius, is stretched half as far as bar A. What is the value of Young's modules for bar B, compared to that of Bar A?
Yb = 1/2 Ya
is it possible for the temperature of a gas to rise without heat flowing into the gas?
Yes, provided that the gas is compressed.
A cylinder with a movable piston contains 0.016 mol of Helium. The gas is expanded as illustrated in the figure below. During this process: a. what is the change in thermal energy of the gas? b. what is the work done by the gas? c. how much heat was added to or removed from the gas? Was it added or removed?
a. 3/2(PfVf-PiVi) 10^-3*300*200 b. 1/2bh+bh c. add both answers together
a satellite is said to be in geosynchronous orbit if it rotates around the earth once every day. a. what is the speed of a satellite at this orbit? b. what is the magnitude of the acceleration felt by a geosynchronous satellite?
a. V = 2pi(R)/t b. a = v^2/r
a particular primate is capable of a remarkable vertical leap, reaching a vertical height of H = 2.1m. a. What is the primate's take-off speed from the ground, in terms of given parameters? b. What is the numerical value of his take-off speed?
a. Voy = square root (2gH) b. calculate speed
a particle rotates in a circle with a centripetal acceleration of a = 10 m/s2. What is the magnitude of the acceleration (a) if: a. the radius is doubled without changing the particle's speed? b. the speed is doubled without changing the circle's radius?
a. a= v2/r b. a = v2/r
the figure shows the velocity vs. time graph of a particle moving along the x-axis. At = 0s, x= 0m. a. At t=3s, what is the particle's acceleration? b. at t=3s, what is the particle's velocity? c. at t=3s, what is the particle's position?
a. a=v/t b. from the graph c. x= area under the curve.
a traffic light is hung at the end of uniform pole AB of length L = 7.0 m A massless cable is attached from point C to D and makes an angle of theta = 37. a. What is the mass (m) of the traffic light? b. what is the horizontal component of the force on the hinge at point A? c. what is the vertical component of the force on the hinge at point A?
a. m = T (height given) - Mg (1/2)*sin of angle divided by g (l) sin 53 b. Fn = T C. Fv = (M + M)(g)
when jumping, you take off at an angle of 30 and land on level ground 0.60s later. a. what is the y-component of your take-off velocity? b. what is the x-component of your take-off velocity? c. what is the length of your jump? d. what is the magnitude of your velocity just before you land on the ground?
a. top vy = 0 top = 1/2(t) voy = g(t) b. Vo= Voy/sintheta Vox = Vo cos theta c. delta x = vo(t) d. Vf = square root (vfx^2+vfy^2)
a 75 kg skier accelerates from rest to a speed of 12 m/s in 3.0 seconds on a frictionless hill. A. what is the slope of the hill? b. what distance does he travel down the hill during the 3.0 seconds?
a. v = vo + a(t) a = v-vo/t a = g sin (theta) theta = sin (a/g) b. x = vo(t) + 1/2 at^2
a package starts at the top of 1.2 m high.. a. what is the initial velocity for the projectile motion? b. what is the height of the platform?
a. v^2 = vo^2 + 2a(x) b. x =vo(T) solve for T y = vo(t)+1/2a(t^2)
A m = 2.00 kg block is held at rest on an incline of angle theta by horizontal force F applied in the direction (parallel to the ground) as shown in the figure. If the coefficient of static friction between block and incline is coefficient = 0.3, determine the minimum value of F to keep the block from moving. b. find the normal force on the block c. find F in terms of the parameters d. plug in values and get answer
b. N = mg cos theta + F sin theta c. F = mgsintheta-coefficientmgcostheta/coeficcientsintheta + costheta
a ball is thrown upwards with the same initial speed from the same height. b. what is the ball's speed just before it hits the ground? c. how long does the ball take to reach the ground? d. what is the total distance travelled by the ball?
b. vy^2 = voy^2-2gy c. vy=voy-gy *Vo is positive d. vy^2=voy^2-2g(y) solve for y initial distance + 2y
a ball is thrown down vertically with an initial speed of 10.0 m/s from a height of 200.0m. b. what is the ball's speed just before it hits the ground? c. how long does the ball take to reach the ground?
b. vy^2= Voy^2-2g(y) c. Vy=Voy-gt *Vo is negative
which ones of the normal forces in the examples shown is/are greatest in magnitude?
cancel out the forces and look at the magnitude.
An ultracentrifuge is often used in biological labs to separate and analyze proteins. What is the net force on a 10 gram sample, which is 10 cm from the axis of the centrifuge's rotor, spinning at 4000 rpm?
change rpm to rad/s x rpm * 2pi/rev*min/60s= rad/s F = mw2r
A NATO base building is warmed using a heat pump that uses 44 F ocean water as the cold water reservoir. Heat extracted from the ocean water warms fluid to 176 F; this warmed fluid is used to heat the building. When the system is working at full capacity, 2000 kW of heat are delivered to the building to warm it at a cost of 600 kW of electric energy. a. what is the actual coefficient of the system? b. what is the theoretical maximum coefficient of performance?
convert Tc and Th to Kelvin. a. COP = Qh/Win b. COP max= TH/TH-TC
a cannonball was launched from the ground with an initial speed v at a directional angle theta. It lands on the ground at a horizontal distance R away from the launch position. If air resistance is negligible, the cannonball's speed during its flight, is at its maximum
during launch and directly before hitting the ground.
Planet X has free-fall acceleration 9 m/s2 at the surface. Planet Y has three times the mass and three times the radius of planet X. On Planet Y, the free fall acceleration is...
g = GM/ R2
the six situations with the cars
if arrows are the same direction, final minus initial. if opposition direction, add them
which of the following statements about acceleration is/are always true? i. if the acceleration of an object is negative, it is slowing down. ii. if an object is moving at a constant speed, its acceleration is zero. iii. if the velocity and acceleration of a moving object are in the same direction, the object is speeding up.
if the velocity and acceleration of a moving object are in the same direction, the object is speeding up.
when a ball is thrown straight up with no air resistance, the acceleration at its highest point __________.
is downward
Which of the following statements about acceleration is/are always true? i. the direction of the acceleration of an object is the same as its velocity. ii. it is possible for an object to have a nonzero acceleration while maintaining a constant speed. iii. if a moving object's acceleration is zero, it is traveling along a straight line.
it is possible for an object to have a nonzero acceleration while maintaining a constant speed and if a moving obejct's acceleration is zero, it is traveling along a straight line.
consider a hypothetical device that takes 10K Jof heat from a hot reservoir (600 K) and expels 7000 J of heat to a cold reservoir (450K) while produces 3000 J of work. What can be said about this device?
it violates the second law of thermodynamics but now the first law.
a 25 kg child bounces on a pogo stick, which has a spring constant k. At the bottom of the bounce she is accelerating upwards at 9.8 m/s.
kdeltax-mg= ma k = m (g+a)/delta x k = 2mg/x
two blocks are connected by a light string passing over a pulley. The block with mass slides on the frictionless horizontal surface, while the block with mass m2 hangs vertically. The tension in the string is
less than mg
a thermally isolated system is made up of a hot piece of aluminum and a cold piece of copper, with the aluminum and the copper in thermal contact. The specific heat capacity of aluminum is more than double that of copper. Which object experiences the greater magnitude gain or loss of heat during the time the system takes to reach thermal equilibrium?
neither one; both of them experience the same size gain or loss of heat.
a block of mass m slides down a rough incline with constant speed. If a similar block that has a mass of 4m were placed on the same incline. it would
slide down at constant speed.
in a cannon demonstration, what was the velocity of the ping pong ball immediately before the collision?
solve for time with the after projectile motion stuff t= square root of -2y/g and then solve for v by delta x/t then vbi= (mball + mass of can/mass of ball) * v
a car is driven at a constant speed over a circular hill and then into a circular valley with the same radius. At the top of the hill the normal force on the driver from the car seat is 50N. the driver's mass is 80kg. What is the magnitude of the normal force on the driver?
top = m(V^2/R) = mg - N (N given in problem So ... bottom N - mg = m(v2/R[same as top]) so top answer + mg = N
a crate is sliding down an inclined ramp at a constant speed of 0.55 m/s. The vector sum of all forces acting on this crate must point ______.
trick question: sum of forces is 0.
suppose you press your physics book against a wall hard enough to keep it from moving. In what direction does the friction force on the book point?
up
a very light ideal spring having a spring constant (force constant) of 6.0 N/cm is used to lift a 2.0-kg rock with an upward acceleration of 2.2 m/s2. If the spring has negligible length when it is not stretched, how long is it while it is pulling the tool upward?
x = m(g+a) / k
an object starts from rest and undergoes uniform acceleration. During the first second it travels 4.0 m. How far will it travel during the third second?
x = vo(t)+1/2at^2 [solve for a] v = vo+a(t) [solve for v] x = vo + 1/2a(t^2)
the two boxes are on a frictionless surface. They had been sitting together at rest, but an explosion between them has just pushed them apart How fast is the 2-kg box going?
Box 1 = Box 2
a 900 N crate slides 12 m down a ramp that makes an angle of 35 with the horizontal. If the crate slides at a constant speed of 2 m/s, how much thermal energy is created?
-mgh-wf=-mgLsintheta
launching on gravity alone? apparent weight?
0 N = free fall
gas held within a chamber passes through the cycle shown in the figure. The area enclosed within the PV diagram is 20.0 J. Determine the energy transferred by the system as heat during the isochoric process if process BC is adiabatic and the energy leaving system as heat during the isobaric process is 7.0 J.
Qab+Qbc+Qca = 20J Qab= total - Qbc+Qac
the top block is accelerated across a frictionless table by the falling mass m. The string is massless, and the pulley is both massless and frictionless. The tension in the string is
T < mg
an object of mass 850g hanging from a rope moves at a constant speed downward. What is the magnitude of the tension of the rope?
T-mg = 0
Two planets orbit a star. You can ignore the gravitational interactions between the planets. Planet 1 has orbital radius r1 and planet 2 has r2 = 9r1. Planet 1 orbits with period T1 Planet 2 orbits with period
T2 = 27 Ti
imagine a carnot engine that operates between a hot and a cold reservoir. Its hot reservoir is at a temperature of tH = 577C. This engine performs 1200 of work and exhausts 655 J of energy as heat to the cold reservoir, each complete cycle. What is temperature of the cold reservoir?
TH = celsius + kelvin Tc = ? e = Wout[workperformed]/Qc+Wout[exhausted] emax = 1-Tc/TH 1-emax is Tc/Th Tc=ratioTh convert Tc to Kelvin
which of the following velocity vs time graphs(s) corresponds to the given force vs time graph. The particle is initially moving to the left.
The graph have the line under the zero line (negative axis).
a piece of ice, initially at rest, starts to slide a distance (L=2.0m) down a roof which has an unknown incline angle onto the horizontal gutter. It then slides horizontally off the gutter and lands a distance D = 2.5m from the house. The vertical distance from the gutter to the ground, H = 3.0m. a. what was the horizontal speed with which the piece of ice slid off the gutter in terms of known parameters? c. what is the numerical value of the acceleration of the ice as it slid along the incline roof? d. what is the numerical value of the incline angle of the roof?
t = square root (2H/g) x= vo (t) Vox = d *square root g/2H c. v^2-vo^2 = 2a(x) = 2g sin (L) a = v^2-vo^2/2L d. a = g sin(theta) theta = sin-1 (a/g)
Which vector best represents the net force acting on the car?
the E the arrow pointing down diagonally.
a particle is moving along the x-axis in the negative direction and is slowing down. We can conclude that
the acceleration is positive.
a mosquito hits the windshield of a car moving at highway speeds and is splattered. Compared with the magnitude of the force and acceleration felt by the car:
the mosquito experiences the same force and a larger acceleration.
the pressure-volume graph shows three paths in which a gas expands from an initial state A to a final state b. The change in internal energy is the same for each of the paths. Rank the paths according to the heat Q added to the gas, smallest to largest.
the one that is in the bottom going down, the one that is diagonal, and then the one going to the top is the biggest one.
The figure shows a graph of position-versus-time date of a toy car. Estimate the car's velocity at 2.0s.
the slope of the tangent line.