Physics Exam

A baseball is hit straight up with an initial vertical velocity of 30 m/s. Ignoring drag, how high does the baseball go?

(Vf)^2 = (Vi)^2 + 2a(delta X) =46m

A 0.14-kg baseball is dropped from rest from a height of 2.0 m above the ground. What is the magnitude of its momentum just before it hits the ground if we neglect air resistance?

(Vf)^2 = (Vi)^2 + 2ax(delta x) (Vf)^2 = (0)^2 + 2(9.8)(2) Vf = 6.26 m/s P= m * v P = .14 * 6.26 = .88

A speeding car, going 40 m/s passes a police officer who is initially stationary in her car. The instant the speeding car passes the officer, the officer starts accelerating at 2m/s^2. If the police officer's acceleration is constant, how far will she have gone when she catches up to the speeding car? (short answer)

(Vf)^2 = (Vi)^2 +2ax(delta t) =400m

A 2 kg ball within initial velocity of v = 10 m/s bounces off of a wall, after the bounce moving in the opposite direction with half its original speed. What is the change in the x-component of the momentum of the ball?

(delta)Px = Pfx - Pix (delta)Px = mVfx - mVix Px = 2(-5) - 2(10) Px = -30 kg * m/s

A 1000-kg cannon suddenly fires a 100-kg cannonball at 50 m/s. What is the recoil speed of the cannon? Assume that frictional forces are negligible and the cannon is fired horizontally.

0 = Pf - Pi 0 = (1000 + 100)v - (100 * 50) 0 = 1100v - 5000 v = 5m/s

The sum of two vectors of fixed magnitudes has the greatest magnitude when the angle between these two vectors is...

0 degrees

A 50-kg skier pushes off the top of a frictionless hill. If after dropping 10 m in elevation, she is moving at 15 m/s, what was her initial speed? Air resistance is negligible.

1/2*m*Vi^2 + m*g*h = 1/2*m*v^2 25Vi^2 + 4900 = 5625

If you wrote the number 10^100 in the standard format as a I followed by a bunch of zeros, how many zeroes would you have to write?

100

A car travels a distance of 25 km in 30 minutes. If it maintains the same velocity, how far does it go in 3 hours?

150 km

You decide to move your washer (50.0 kg) and dryer (30.0 kg) together to a new location, so you push on the washer, which simultaneously pushes on the dryer. If there is no friction or drag, what is the net force on the washer if you push it with a force of 20.0 N?

20 = (50kg + 30kg) = a a = .25 m/s^2 F = (50.0) * .25 F = 12.5N

A vector (v) has a direction that is 30° above the x-axis and a magnitude of 10 m/s. The x andy components of the vector are

8.7m/s, 5.0m/s

Two kids in a school bus are playing catch with a baseball. The ball is thrown from the front to the back of the bus with a speed of 20 m/s, as seen from the inside the bus. If the bus is moving in the +x-direction with a velocity of 10 m/s as seen from the ground, what is the velocity of the ball as seen from the ground?

<--- -20m/s (going right) + 10m/s --> (going left) =-10m/s

An ideal incompressible fluid flows through a 4.0-cm-diameter pipe at 1.0 m/s. There is a 2.0 cm diameter constriction in the line. What is the speed of the fluid in this constriction?

A1v1 = A2v2 convert to meters and solve for areas then solve for v2 =4.0 m/s

Which of the following situations is impossible? a) An object has velocity directed east and acceleration directed west. b) An object has velocity directed east and acceleration directed east. c) An object has constant non-zero acceleration and changing velocity. d) An object has constant non-zero velocity and changing acceleration. e) An object has zero velocity but non-zero acceleration.

An object has constant non-zero velocity and changing acceleration.

Two frisky otters slide down frictionless hillsides of the same height but different slopes. The slope of the hill of otter 1 is 30°, while the slope of the hill of otter 2 is 60°. If both start from rest, which otter is moving faster when she reaches the bottom of her hill? A. Otter 1 is moving faster. B. Otter 2 is moving faster. C. The heavier otter is moving faster, no matter which hill she used. D. The otter that took the shorter time is moving faster. E. Both otters have the same speed at the bottom.

Both otter have the same speed at the bottom

A 450-kg sports car accelerates from rest to 1 00 km/h in 4.80 s. What magnitude force does a 68.0 kg passenger experience during the acceleration?

Convert 100km/h to m/s divide by seconds given in problem multiply by weight of the passenger =394N

A person weighing 900 N is standing on snowshoes. Each snowshoe has area 2500 cm2 and has negligible weight. What pressure does this person's weight exert on the snow?

Convert to m^2 --> .25 m^2 Divide person's weight by area --> 3600 N/m^2 THEN divide pressure by two since there are two snowshoes --> 1800 N/m^2

If the collision between Erica and Danny lasts 0.2 seconds, what is the average force experience by each person during the collision (magnitudes and directions)? Don't include the force of gravity.

Danny: (delta)P = (30kg * 1.2) - (30kg * 0) = 36 Erica (delta)P = (20kg * 1.2) - (20kg * 3) = -36 (delta)P = J = Fave/(delta)t Fave = (delta)P/(delta)t Danny: Fave = 36 kg*m/s / 0.2s = 180N Erica: Fave = -36 kg*m/s / 0.2s = -180N

A skydiver with an area A = 2.0 m^2 falls through the air at a constant terminal speed of 40 m/s. What is the mass of the skydiver?

Drag problem D = 1/4*p*A*v^2 D = 1/4(1.2)(2.0)(40)^2 D = 960 D = Mg 960 = M (9.8) M = 98 kg

A satellite is in orbit around the earth. Which one feels the greater force?

Earth and the satellite feel exactly the same force.

A cylinder of solid iron is supported by a string while submerged in water. If the tension in the string is 43 N, what is the mass of the iron cylinder? The density of iron is 7860 kg/m^3 and that of water is 1000 kg/m^3. Hint: Use V = M/P(iron) in the buoyant force.

Fnet = T - Mg + Fb = 0 V = M/P(iron) Fb = pf * V * g Fb = pf * M/P(iron) * g T - Mg + pf * M/P(iron) * g = 0 M = T/g(1-pf/p) M = 43/9.8(1-1000/7860) M = 5.0 kg

A block with a mass of 10kg is pulled across the ground at a constant speed. If the rope is pulled at an angle of 45 degrees with respect to the horizontal and the coefficient of friction is 0.4 what is the tension (T) on the rope?

Fnetx = -ukN + Tcos(45) = 0 Fnety = N - Mg + Tsin(45) = 0 N = Mg - Tsin(45) --> input into Fnetx equation 0 = -uk(Mg-Tsin(45)) + Tcos(45) ukMg = T(cos(45) + uksin(45)) T= ukMg/(cos(45) + uksin(45))

Which of the following is not a contact force? A. Friction B. Normal force C. Drag force D. Force of gravity E. Spring force

Force of gravity

The maximum force that a window on a submarine can withstand is 10^7 N. If the area of the window is 0.2 m2, approximately what is the maximum depth that the submarine can safely dive without the window breaking? The density of sea water is 1025 kg/m3.

Hydrostatic pressure = p0 + pgd P = p * g * d Take force and divide by area of window to get pressure = 5 * 10^7 5 * 10^7 = 1025 * 9.8 * d d = 5km

A rock is thrown from the upper edge of a tall cliff at some angle above the horizontal. It reaches its highest point and starts falling down. Which of the following statements about the rock's motion are true just before it hits the ground? A. Its horizontal velocity component is the same as it was just as it was launched. B. Its speed is the same as it was just as it was launched. C. Its velocity is vertical. D. Its vertical velocity component is the same as it was just as it was launched. E. Its horizontal velocity component is zero.

Its horizontal velocity component is the same as it was just as it was launched.

James and John dive from an overhang into the lake below. James simply drops straight down from the edge. John takes a running start and jumps with an initial horizontal velocity of 25 m/s. Compare the time it takes each to reach the lake below if there is no air resistance.

James and John will reach the surface of the lake at the same time.

Two moving cars collide and stick together. Which of the following is not conserved during the collision. A. total momentum B. total energy C. kinetic energy D. all are conserved E. None are conserved

Kinetic energy

A very light ping-pong ball moving east at a speed of 4 m/s collides with a very heavy stationary bowling ball. The Ping-Pong ball bounces back to the west, and the bowling ball moves very slowly to the east. Which object experiences the greater magnitude impulse during the collision? A. Neither; both experience the same magnitude impulse during the collision B. The ping-pong ball C. The bowling ball D. It is impossible to tell since the actual masses and velocities are not given

Neither; both experience the same magnitude impulse during the collision

A crate is sliding down an inclined ramp at a constant speed of 0.55 m/s. The vector sum of all the forces acting on this crate must point.... A. down the ramp. B. perpendicular to the ramp. C. up the ramp. D. None of the above choices is correct

None of the above choices is correct

A firecracker in a coconut blows the coconut into three equal pieces. Two pieces fly off south and west, perpendicular to each other, at 1 0 m/s. Which direction is the third piece moving? A. Due North B. Due East C. North-East D. It is not moving

North-East

A flatbed truck is carrying a 20.0-kg crate along a level road. The coefficient of static friction between the crate and the bed is 0.400, and the coefficient of kinetic friction is 0.300. What is the maximum acceleration that the truck can have if the crate is to stay in place relative to the truck?

Only need to coefficient of static friction F = ma = Fs 78.48 = (20kg) (a) a = 3.92 m/s

In a section of horizontal pipe with a diameter of 3.0 cm, the pressure is 100 kPa and water is flowing with a speed of 1.5 m/s. The pipe narrows to 2.0 cm. What is the pressure in the narrower region? Treat the water as an ideal incompressible fluid. The density of water is 1000 kg/m3. (1 kPa = 1000 Pa)

P1 = P2 convert pressure to Pa P1 + 1/2 * p * vi^2 = 1.011 * 10^5 A1v1 = A2v2 find areas, solve for v2 P2 + 1/2 * 1000 * v2(above) = 1.011 x 10^5 P2 =95 kPa

Danny (30 kg) and Erica (20 kg) are bouncing on a trampoline. Just as Danny reaches the high point of his bounce, Erica is moving upward past him at 3.0 m/s. At that instant she grabs hold of him. What is their speed just after she grabs him?

Pf = Pi Pi(Erica) = mv = 20(3.0) = 60 = Pf Pi(Danny) = 30(0) = 0 60 = (Me + Md) * v v = 1.2 m/s

A rock from a volcanic eruption is launched straight up into the air with no appreciable air resistance. Which one of the following statements about this rock while it is in the air is correct? a) The acceleration is downward at all points in the motion. b) The acceleration is downward at all points in the motion except that is zero at the highest point. c) On the way up, its acceleration is downward and its velocity is upward, and at the highest point both its velocity and acceleration are zero. d) Throughout the motion, the acceleration is downward, and the velocity is always in the same direction as the acceleration. e) On the way down, both its velocity and acceleration are downward, and at the highest point both its velocity and acceleration are zero.

The acceleration is downward at all points in the motion

A baseball player runs from 3rd base and slides into home, coming to rest at the home plate. Where did most of the runner's kinetic energy go when he slide into home plate? A. Gravitational potential energy B. Thermal energy C. Chemical energy D. Nowhere. The runner's kinetic energy was conserved.

Thermal energy

Which of Newton's three laws of motion involves equal and opposite force pairs? A. First Law B. Second Law C. Third Law D. None

Third Law

About how long does it take the baseball in problem 23 to return to the ground?

Vf = Vi + a(delta t) = 6s

A traveler pulls on a suitcase strap at an angle 30° above the horizontal. If 300 J of work are done by the strap while moving the suitcase a horizontal distance of 10 m, what is the tension in the strap?

W = F * dcos() 300 = F * 10cos(30) F = 35N

When is the total momentum of a system not conserved? A. When there are only internal forces. B. When there is a non-zero net external force. C. When the net external forces is zero D. Never

When there is a non-zero net external force

A policeman investigating an accident measures the skid marks left by a car on the horizontal road. He determines that the distance between the point that the driver slammed on the brakes (thereby locking the wheels) and the point where the car came to a stop was 28.0 m. From a reference manual he determines that the coefficient of kinetic friction between the tires and the road under the prevailing conditions was 0.300. Now fast was the car going when the driver applied the brakes?

Work friction = F(friction) * 28m F(friction) = uk * m * g KE = 1/2 * m * v^2 uk * m * g * 28m = 1/2 * m * v^2 mass cancels uk * g * 28m = 1/2 * v^2 solve for v =12.8

A penny is dropped off of a tall bridge and free falls towards the water far below. At t = 0 s, its initial velocity is zero and its position is y 0 rn, where the +y direction is vertically upward. Ignoring drag, draw a graph of the position versus time, clearly labeling the axes and showing times between 0 and 5 seconds. (short answer)

Xf = Xi + Vxi (delta t) + 1/2 ax (delta t)^2 y = 1/2 * 9.8 m/s^2 * t^2 t=0 --> y=0m t=1 --> y=-5m t=2 --> y=-20m t=3 --> y=-30m draw graph...

A car goes at a constant speed of v = 25 m/s around a circular track with a radius r = 150 m. What is its centripetal acceleration experienced by the car (magnitude and direction)?

a = v^2/r =4.2 towards the center of the track

An auto manufacturer advertises that their car can go "from zero to sixty in eight seconds." This is a description of what characteristic of the car's motion?

average acceleration

A diver jumps from a cliff and hits the water with a vertical velocity Vy=-15m/s. After entering the water, the diver quickly comes to a stope in 0.5 seconds. What is the average acceleration experienced by the diver (magnitude and direction) while coming to a stop.

ay = Vyf - Viy/(delta t) = 30m/s directed upwards

A 1938 nickel has a diameter of 21.21 mm, a thickness of 1.95 mm, and weighs 0.04905 N. What is its density?

convert to meters V = pi * r^2 * h solve for mass from the weight divide mass by volume to get density

Two displacement vectors have magnitudes of 5.0 m and 7.0 m, respectively, if these two vectors are added together, the magnitude of the sum...

could be as small as 2.0 m or as large as 12 m.

An object moving in the +x direction experiences an acceleration of 2 m/s^2 this means the object...

is increasing its velocity by 2.0 m/s every second.

By pulling down on a (massless) rope placed over a massless frictionless pulley, a 5.0kg bucket of water is lifted out of a well with an upward acceleration of 3.0 m/s^2. What is magnitude of the force pulling down on the rope.

m*a = T - W m*a = T - Mg 5.0 * 3.0 = T - (5.0 * 9.8) T = 64

A vector is a quantity that has what properties?

magnitude and direction

Which of the following is not a vector quantity?

speed

The wind is blowing at 10 m/s in a northerly direction. This quantity is the wind's

velocity

When is the average velocity of an object equal to the instantaneous velocity?

when the velocity is constant

A football kicker is attempting a field goal from 44 m out. The ball is kicked and just clears the lower bar with a time of flight of 2.9 s. If the angle of the kick was 45°, what was the initial speed of the ball, assuming no air resistance?

x = Vix + t Vix = Vi * cos(45) 44 = Vi * cos(45) + 2.9 Vi = 21.5 m/s