Physics 2010 final

A meter stick is supported by a knife edge at the 50-cm mark. Doug hangs masses of 0.40 and 0.60 kg from the 20-cm and 80-cm marks, respectively. Where should Doug hang a third mass of 0.30 kg to keep the stick balanced?

(30 cm)

Calculate (0.82 + 0.042) (4.4 103 ), keeping only significant figures.

3 800

Which one of the choices below represents the preferred practice regarding significant figures when adding the following: 12.4 + 11 + 67.37 + 4.201?

95

Two billiard balls have velocities of 2.0 m/s and 1.0 m/s when they meet in an elastic head-on collision. What is the final velocity of the first ball after collision?

(-1.0 m/s)

A hill is 100 m long and makes an angle of 12 with the horizontal. As a 50-kg jogger runs up the hill, how much work does gravity do on the jogger?

(-10 000 J)

Alex, parked by the side of an east-west road, is watching car P, which is moving in a westerly direction. Barbara, driving east at a speed 52 km/h, watches the same car. Take the easterly direction as positive. If Alex measures a speed of 78 km/h for car P, what velocity will Barbara measure?

(-130 km/h)

. A drag racer starts from rest and accelerates at 10 m/s2 for the entire distance of 400 m (1/4 mile). What is the velocity of the race car at the end of the run?

(89 m/s)

A ceiling fan is turned on and reaches an angular speed of 120 rev/min in 20 s. It is then turned off and coasts to a stop in an additional 40 s. The ratio of the average angular acceleration for the first 20 s to that for the last 40 s is which of the following?

(-2)

Which one, temperature, velocity, acceleration, or displacement, is not a vector quantity?

(temperature)

A horizontal force of 200 N is applied to a 55-kg cart across a 10-m level surface. If the cart accelerates at 2.0 m/s2 , then what is the work done by the force of friction as it acts to retard the motion of the cart?

(-900 J)

A cheetah can run at approximately 100 km/hr and a gazelle at 80.0 km/hr. If both animals are running at full speed, with the gazelle 70.0 m ahead, how long before the cheetah catches its prey?

(12.6 s)

An 80-kg man is one fourth of the way up a 10-m ladder that is resting against a smooth, frictionless wall. If the ladder has a mass of 20 kg and it makes an angle of 60 with the ground, find the force of friction of the ground on the foot of the ladder.

(170 N)

A girl and her bicycle have a total mass of 40.0 kg. At the top of the hill her speed is 5.0 m/s, and her speed doubles as she rides down the hill. The hill is 10.0 m high and 100 m long. How much kinetic energy and potential energy is lost to friction?

(2 420 J)

A 4.0 kg ball is moving at 3.0 m/s to the NORTH and a 5.0 kg ball is moving at 2.0 m/s to the NORTHWEST. What is the total momentum of the system?

(20.3 kg m/s at an angle of 69.7 degrees NORTH of WEST)

A stone is thrown with an initial speed of 15 m/s at an angle of 53 above the horizontal from the top of a 35 m building. If g = 9.8 m/s2 and air resistance is negligible, then what is the magnitude of the vertical velocity component of the rock as it hits the ground?

(29 m/s)

A 100-W light bulb is left on for 10.0 hours. Over this period of time, how much energy was used by the bulb?

(3 600 000 J)

A 10.0-kg box starts at rest and slides 3.5 m down a ramp inclined at an angle of 10 with the horizontal. If there is no friction between the ramp surface and crate, what is the velocity of the crate at the bottom of the ramp?

(3.5 m/s)

A 0.30-m-radius automobile tire accelerates from rest at a constant 2.0 rad/s2 . What is the centripetal acceleration of a point on the outer edge of the tire after 5.0 s?

(30 m/s2 )

A stone is thrown with an initial speed of 15 m/s at an angle of 53 above the horizontal from the top of a 35 m building. If g = 9.8 m/s2 and air resistance is negligible, what is the magnitude of the horizontal displacement of the rock?

(38 m)

A car drives around a curve with radius 400 m at a speed of 32 m/s. The road is banked at 7.0 degree. The mass of the car is 1500 kg. What is the magnitude of the centripetal force in order to make this turn?

(3800 N)

A 1 200-kg automobile moving at 25 m/s has the brakes applied with a deceleration of 8.0 m/s2 . How far does the car travel before it stops?

(39 m)

A 4.0 kg object is moving at 5.0 m/s NORTH. It strikes a 6.0 kg object at rest. The objects have an elastic collision and move is the NORTH or SOUTH direction. What is the velocity of the 6.0 kg object after the collision?

(4.0 m/s NORTH)

A rock is thrown straight up with an initial velocity of 19.6 m/s. What time interval elapses between the rock's being thrown and its return to the original launch point?

(4.00 s)

A 1 000-kg sports car accelerates from zero to 25 m/s in 7.5 s. What is the average power delivered by the automobile engine?

(41.7 kW)

A 2 000-kg sailboat experiences an eastward force of 3 000 N by the ocean tide and a wind force against its sails with magnitude of 6 000 N directed toward the northwest (45 N of W). What is the direction of the resultant acceleration?

(74 N of W)

A 500-N tightrope walker stands at the center of the rope. If the rope can withstand a tension of 1 800 N without breaking, what is the minimum angle the rope can make with the horizontal?

(8)

A river flows due east at 3.0 m/s. A boat crosses the 300-m-wide river by maintaining a constant velocity of 10 m/s due north relative to the water. If no correction is made for the current, how far downstream does the boat move by the time it reaches the far shore?

(90 m)

The number 0.00017 has how many significant figures?

2

Which one of the choices below represents the preferred practice regarding significant figures when multiplying the following: 10.5 *8.8 * 3.14?

290

If the length of a box is educed to one-third of its original value and the width and height are doubled, by what factor has the volume changed?

3/2

A ball is pushed with an initial velocity of 4.0 m/s. The ball rolls down a hill with a constant acceleration of 1.6 m/s2 . The ball reaches the bottom of the hill in 8.0 s. What is the ball's velocity at the bottom of the hill?

(17 m/s)

. A block of mass 5.00 kg rests on a horizontal surface where the coefficient of sliding kinetic friction between the two is 0.200. A string attached to the block is pulled horizontally, resulting in a 2.00-m/s2 acceleration by the block. Find the tension in the string.

(19.8 N)

A plane is moving due north, directly towards its destination. Its airspeed is 200 mph. A constant breeze is blowing from west to east at 30 mph. At what rate is the plane moving north?

(198 mph)

A 15-kg block rests on a level frictionless surface and is attached by a light string to a 5.0-kg hanging mass where the string passes over a massless frictionless pulley. If g = 9.8 m/s2 , what is the tension in the connecting string?

(37 N)

Doug hits a hockey puck, giving it an initial velocity of 6.0 m/s. If the coefficient of kinetic friction between ice and puck is 0.050, how far will the puck slide before stopping?

(37 m)

An object of mass m moving at speed v0 strikes an object of mass 4m which had been at rest. The first object bounces backward along its initial path at speed v0. Is this collision elastic, and if not, what is the change in kinetic energy of the system?

(No, the kinetic energy increased by ½ mv2 .)

An astronaut applies a force of 500 N to an asteroid and it accelerates at 7.00 m/s2 . What is the asteroid's mass?

(71 kg)

A baseball is released at rest from the top of the Washington Monument. It hits the ground after falling for 6.0 s. What was the height from which the ball was dropped? Ignore air resistance.

(1.8 x 102 m)

A boat moves at 10.0 m/s relative to the water. If the boat is in a river where the current is 2.00 m/s, how long does it take the boat to make a complete round trip of 1 000 m upstream followed by a 1 000-m trip downstream?

(208 s)

A 60-kg woman runs up a flight of stairs having a rise of 4.0 m in a time of 4.2 s. What average power did she supply?

(560 W)

A 10-kg mass and a 2.0-kg mass are connected by a light string over a massless, frictionless pulley. If g = 9.8 m/s2 , what is the acceleration of the system when released?

(6.5 m/s2 )

A golf ball hits a wall and bounces back at 3/4 the original speed. What part of the original kinetic energy of the ball did it lose in the collision?

(7/16)

A 0.30-m-radius automobile tire accelerates from rest at a constant 2.0 rad/s2 over a 5.0-s interval. What is the tangential component of acceleration for a point on the outer edge of the tire during the 5-s interval?

(0.60 m/s2 )

A 7.0-kg bowling ball experiences a net force of 5.0 N. What will be its acceleration?

(0.71 m/s2 )

A cannon of mass 1 500 kg fires a 10-kg shell with a velocity of 200 m/s at an angle of 45 above the horizontal. Find the recoil velocity of the cannon across the level ground.

(0.94 m/s)

A 2 500-kg truck moving at 10.00 m/s strikes a car waiting at a traffic light, hooking bumpers. The two continue to move together at 7.00 m/s. What was the mass of the struck car?

(1 070 kg)

A 500-N tightrope walker stands at the center of the rope such that each half of the rope makes an angle of 10.0 with the horizontal. What is the tension in the rope?

(1 440 N)

Two ropes are attached to a 40-kg object. The first rope applies a force of 25 N and the second, 40 N. If the two ropes are perpendicular to each other, what is the resultant acceleration of the object?

(1.2 m/s2 )

If the kinetic energy of a ball is doubled, what happens to the momentum of the ball?

(1.41 times larger)

A 0.12-m-radius grinding wheel takes 5.5 s to speed up from 2.0 rad/s to 11.0 rad/s. What is the wheel's average angular acceleration?

(1.6 rad/s2 )

A 0.12-kg ball is moving at 6 m/s when it is hit by a bat, causing it to reverse direction and have a speed of 8 m/s. What is the change in the magnitude of the momentum of the ball?

(1.68 kg m/s)

A horizontal force of 750 N is needed to overcome the force of static friction between a level floor and a 250-kg crate. What is the acceleration of the crate if the 750-N force is maintained after the crate begins to move and the coefficient of kinetic friction is 0.12?

(1.8 m/s2 )

Two blocks, joined by a string, have masses of 6.0 and 9.0 kg. They rest on a frictionless horizontal surface. A 2nd string, attached only to the 9-kg block, has horizontal force = 30 N applied to it. Both blocks accelerate. Find the tension in the string between the blocks.

(12 N)

A rock, released at rest from the top of a tower, hits the ground after 1.5 s. What is the speed of the rock as it hits the ground? Ignore air resistance.

(15 m/s)

A 0.400-kg object is swung in a circular path and in a vertical plane on a 0.500-m-length string. If the angular speed at the bottom is 8.00 rad/s, what is the tension in the string when the object is at the bottom of the circle?

(16.7 N)

. A Cessna aircraft has a lift-off speed of 120 km/hr. What minimum constant acceleration does this require if the aircraft is to be airborne after a take-off run of 240 m?

(2.31 m/s2 )

Human reaction time is usually about 0.20 s. If your lab partner holds a ruler between your finger and thumb and releases it without warning, how far can you expect the ruler to fall before you catch it?

(20 cm)

A railroad freight car, mass 15 000 kg, is allowed to coast along a level track at a speed of 2.0 m/s. It collides and couples with a 50 000-kg loaded second car, initially at rest and with brakes released. What percentage of the initial kinetic energy of the 15 000-kg car is preserved in the two-coupled cars after collision?

(23%)

An elevator weighing 20 000 N is supported by a steel cable. What is the tension in the cable when the elevator is being accelerated upward at a rate of 3.00 m/s2 ?

(26 100 N)

A 30 kg mass falls from a height of 4.0 m. What is the momentum of the mass just before it hits the ground?

(265.6 kg m/s)

A stone is thrown with an initial speed of 15 m/s at an angle of 53 above the horizontal from the top of a 35 m building. If g = 9.8 m/s2 and air resistance is negligible, then what is the speed of the rock as it hits the ground?

(30 m/s)

A rock is thrown straight up with an initial velocity of 24.5 m/s. what maximum height will the rock reach before starting to fall downward? Take acceleration due to gravity as 9.80 m/s2 .

(30.6 m)

Geosynchronous satellites orbit the Earth at a distance of 42 000 km from the Earth's center. Their angular speed at this height is the same as the rotation rate of the Earth, so they appear stationary at certain locations in the sky. What is the force acting on a 1 500-kg satellite at this height?

(339 N)

A 4.0 kg ball is traveling at 5.0 m/s and strikes a wall. The 4.0 kg ball bounces off the wall with a velocity of 4.0 m/s. What is the change in momentum of the ball?

(36 kg m/s)

. A car drives around a curve with radius 400 m at a speed of 32 m/s. The road is not banked. The mass of the car is 1500 kg. What is the frictional force on the car?

(3800 N)

A 20-kg traffic light hangs midway on a cable between two poles 40 meters apart. If the sag in the cable is 0.40 meters, what is the tension in each side of the cable?

(4 900 N)

A boxcar of mass 200 tons at rest becomes uncoupled on a 2.5 grade. If the track is considered to be frictionless, what speed does the boxcar have after 10 seconds?

(4.3 m/s)

A roller coaster, loaded with passengers, has a mass of 2 000 kg; the radius of curvature of the track at the bottom point of the dip is 24 m. If the vehicle has a speed of 18 m/s at this point, what force is exerted on the vehicle by the track?

(4.7 * 104 N)

A 20-N crate starting at rest slides down a rough 5.0-m long ramp, inclined at 25 with the horizontal. 20 J of energy is lost to friction. What will be the speed of the crate at the bottom of the incline?

(4.7 m/s)

A pile driver drives a post into the ground. The mass of the pile driver is 2 500 kg and it is dropped through a height of 8.0 m on each stroke. If the resisting force of the ground is 4.0 106 N, how far is the post driven in on each stroke?

(4.9 cm)

A rod of length L is pivoted about its left end and has a force F applied perpendicular to the other end. The force F is now removed and another force F' is applied at the midpoint of the rod. If F' is at an angle of 30o with respect to the rod, what is its magnitude if the resulting torque is the same as when F was applied?

(4F)

A stone is thrown at an angle of 30 above the horizontal from the top edge of a cliff with an initial speed of 12 m/s. A stop watch measures the stone's trajectory time from top of cliff to bottom to be 5.6 s. How far out from the cliff's edge does the stone travel horizontally? Ignore air resistance.

(58 m)

Alex throws a 0.15-kg rubber ball down onto the floor. The ball's speed just before impact is 6.5 m/s, and just after is 3.5 m/s. If the ball is in contact with the floor for 0.025 s, what is the magnitude of the average force applied by the floor on the ball?

(60 N)

A ceiling fan is turned on and reaches an angular speed of 120 rev/min in 20 s. It is then turned off and coasts to a stop in 40 s. In the one minute of rotation, through how many revolutions did the fan turn?

(60)

A jet airliner moving at 500 mph due east moves into a region where the wind is blowing at 120 mph in a direction 30.0 north of east. What is the new velocity and direction of the aircraft?

(607 mph, 5.67 N of E)

The following force vectors act on an object: i) 50.0 newtons at 45.0 north of east and ii) 25.0 newtons at 30.0 south of east. What is the magnitude of the resultant force and its angle relative to the easterly direction?

(61.4 newton at 21.8)

A railroad train travels forward along a straight track at 80.0 m/s for 1 000 m and then travels at 50.0 m/s for the next 1 000 m. What is the average velocity?

(61.5 m/s)

A cart is given an initial velocity of 5.0 m/s and experiences a constant acceleration of 2.0 m/s2 . What is the magnitude of the cart's displacement during the first 6.0 s of its motion?

(66 m)

A 5 000-N weight is suspended in equilibrium by two cables. Cable 1 applies a horizontal force to the right of the object and has a tension, T1. Cable 2 applies a force upward and to the left at an angle of 37.0 to the negative x axis and has a tension, T2. Find T2.

(8 310 N)

A taxicab moves five blocks due north, five blocks due east, and another two blocks due north. Assume all blocks are of equal size. What is the magnitude of the taxi's displacement, start to finish?

(8.6 blocks)

A horizontal force is applied to a 4.0 kg box. The box starts from rest moves a horizontal distance of 8.0 meters and obtains a velocity of 6.0 m/s. The system is frictionless. What is the horizontal force?

(9 N)

A string attached to an airborne kite is maintained at an angle of 40 with the horizontal. If a total of 120 m of string is reeled in while bringing the kite back to the ground, what is the horizontal displacement of the kite in the process? Assume the kite string doesn't sag.

(92 m)

A force of 5.0 N is applied to a 20-kg mass on a horizontal frictionless surface. As the speed of the mass increases at a constant acceleration, what happens to the power delivered to it by the force? It remains the same, increases, or decreases?

(Increases)

Two particles collide, one of them initially being at rest. Is it possible for both particles to be at rest after the collision?

(No, momentum will not be conserved.)

A 75-kg swimmer dives horizontally off a 500-kg raft. If the diver's speed immediately after leaving the raft is 4 m/s, what is the corresponding raft speed?

(0.6 m/s)

An object moves 20 m east in 30 s and then returns to its starting point taking an additional 50 s. If west is chosen as the positive direction, what is the sign associated with the average velocity of the object?

(0, no sign)

A hiker walks 200 m west and then walks 100 m north. In what direction is her resulting displacement?

(26.6 N of W)

The length and width of a standard sheet of paper is measured, and then the area is found by calculation to be 93.50 in2 . What is the number of significant figures in the width measurement must be at least?

4

A horizontal force of 750 N is needed to overcome the force of static friction between a level floor and a 250-kg crate. If g = 9.8 m/s2 , what is the coefficient of static friction?

(0.31)

An object moves 20 m east in 30 s and then returns to its starting point taking an additional 50 s. If west is chosen as the positive direction, what is the average speed of the object?

(0.50 m/s)

A 100-kg box is placed on a ramp. As one end of the ramp is raised, the box begins to move downward just as the angle of inclination reaches 15. What is the coefficient of static friction between box and ramp?

(0.27)

Tasha has mass 20 kg and wants to use a 4.0-m board of mass 10 kg as a seesaw. Her friends are busy, so Tasha seesaws by herself by putting the support at the center of gravity when she sits on one end of the board. How far is she from the support point?

(0.67 m)

A 20-g bullet moving at 1 000 m/s is fired through a one-kg block of wood emerging at a speed of 100 m/s. If the block had been originally at rest and is free to move, what is its resulting speed?

(18 m/s)

. A stone is thrown at an angle of 30 above the horizontal from the top edge of a cliff with an initial speed of 12 m/s. A stop watch measures the stone's trajectory time from top of cliff to bottom to be 5.6 s. What is the height of the cliff?

(120 m)

A jogger runs halfway around a circular path with a radius of 60 m. What, respectively, are the magnitude of the displacement and the distance jogged?

(120 m, 188 m)

A 20 kg box slides down a 12.0 m long frictionless incline at an angle of 30 degrees with the horizontal. A force of 50 N is applied to the box to try to pull it up the incline. The applied force makes an angle of 10 degrees to the incline and above the incline. What is the increase in the kinetic energy of the box?

(585 J)

Water flows over a section of Niagara Falls at a rate of 1.20 106 kg/s and falls 50.0 m. What is the power dissipated by the waterfall?

(588 MW)

A 2 000-kg sailboat experiences an eastward force of 3 000 N by the ocean tide and a wind force against its sails with magnitude of 6 000 N directed toward the northwest (45 N of W). What is the magnitude of the resultant acceleration?

(2.2 m/s2 )

. When a drag strip vehicle reaches a velocity of 60 m/s, it begins a negative acceleration by releasing a drag chute and applying its brakes. While reducing its velocity back to zero, its acceleration along a straight line path is a constant 7.5 m/s2 . What displacement does it undergo during this deceleration period?

(240 m)

A 5 000-N weight is held suspended in equilibrium by two cables. Cable 1 applies a horizontal force to the right of the object and has a tension, T1. Cable 2 applies a force upward and to the left at an angle of 37.0 to the negative x axis and has a tension, T2. What is the tension, T1?

(6 640 N)