Physics Chapter 6/7
A truck mass of 4000kg is at rest but free to roll with no resistance. If you push it forward with a force of 500N, the momentum at the end of 5s of pushing will be
Impulse = Change In momentum F * T = Pf - Pi 500 * 5 = Pf - 0 500 * 5 = Pf Pf = 2500
Which of the following is possessed by a moving object but not a stationary A). Mass B). Kinetic Energy C.) Inertia D.) Energy
B). Kinetic Energy K.E = 1/2mV^2 So object must be moving!
If the speed of a car is doubled, the work to stop the car changes by a factor of A.) 4 B.) 1 C.) 2 D.) 1/2 E.) 1/4
A.) 4
The kinetic energy of a body is correctly given by which of the following expressions A.) 1/2, mv B.) 1/2, mv^2 C.) mv D.) mv^2 E.) 2 mv^2
B.) 1/2, mv^2 KE = 1/2mv^2
A gun is made of a super low weight but strong material the bullet for the gun is more massive than the gun itself. For such a gun A.) Recoil problems would be lessened B.) The bullet would go farther with less power C.) Conservation of momentum is not satsified D.) The gun if unsupported would have a recoil velocity higher than bullet velocity
D.) The gun if unsupported would have a recoil velocity higher than bullet velocity In case of recoil => Less mass = High Velocity
A box is moved 10M across the floor by a force of 20N acting along the direction of motion. The work done by the force is A.) 100J B.) 20J C.) 2.0J D.) 30J E.) 200J
E.) 200J Work = Force * Distance = 20 * 10 = 200J
A painter of mass 80kg climbs 3.0m up a ladder. The painter's potential energy has increased by A.) 1284J B). 261J C). 240J D.) 784J E.) 2352J
E.) 2352J PE = MGH = 80 * 9.8 * 3 = 2358J
Force F, acting for time T and over a distance of D, gives impulse I. To get the same impulse using half the force it would be necessary for the force to act A.) Over a distance 2D B.) Over a distance 4D C.) For half the time T D.) Over half the distance D E.) For a time 2T
E.) For a time 2T
A wooden block slides down a rough incline which of the following statements is true. A.) The mechanical energy of the block is constant B.) The mechanical energy of the block is increasing C.) The gravitational potential energy of the block is increasing D.) The kinetic energy of the block is decreasing E.) The mechanical energy of the block is decreasing
E.) The mechanical energy of the block is decreasing Rough Surface = > Friction Force As block slides down => -Ve work due to friction => Mechanical energy decreases.
When a baseball hits the bat, the impulse delivered to the ball is increased by A.) "Follow through" on the swing B.) Rapidly stopping the bat after impact C.) Impulse can not be changed D.) Letting the bat coil upon impact
A.) "Follow through" on the swing Impact will be increased by increasing the time of contact
A bullet of mass 0.010kg and speed of 100m/s is brought to rest in a wooden block after penerating a distance of 0.10m. The work done on the bullet by the block is A.) -50J B.) Zero C.) 50J D.) 0.001J E.) -0.001J
A.) -50J KEF-KEI=Work W = -1/2 * 0.01 * 100^2 W= -50J
A 20kg child runs at 4.0m/s and jumps onto a shopping cart , which also has mass 20kg. Assuming the child rides on the cart after the collision, the speed of the child and the shopping cart, just after the child jumps on it is A.) 2.0m/s B.) zero C.) 3.0m/s D.)4.0m/s
A.) 2.0m/s Ptotal intial = Ptotal final 20 * 4 + 20 * 0 = (20+20) vfinal 80 = 40 vf vf = 2.0 m/s
In order for a body to exhibit simple harmonic motion there must be A.) A force drawing the body toward the center and increasing with the distance away from the center B.) A force drawing with the body toward the center and decreasing with the distance away from the center C.) A constant force pushing the body away from the center D.) A constant force drawing the body towards the center E.) A force pushing the body away from the center and increasing with the distance away from the center
A.) A force drawing the body toward the center and increasing with the distance away from the center
A box is pushed across a rough horizontal floor by a force acting parallel to the floor in the direction of motion. A force doing negative work on the body is A.) Friction B). A fictitious force C.) The applied force D.) Gravity E.) Normal reaction to the force of the floor upward on the body
A.) Friction Rough surface = Friction Friction Force is against the motion
The purpose of an air bag in an auto is to A.) Increase your body's stopping time during a collision B.) Reduce your speed just before a collision C.) Reduce the need for good brakes on your car D.)Increase the force applied to you during a collision
A.) Increase your body's stopping time during a collision Impulse = Force * Time As the time increases => Force decreases
A brick slides across a horizontal rough surface and eventually comes to a stop. What happened to the kinetic energy of the brick? A.) It was converted to other forms of energy, mostly heat B). It was converted to a potential energy of friction C.) It was simply destroyed in the process of stopping D.) Nothing, it is still in the brick but now it is called potential energy
A.) It was converted to other forms of energy, mostly heat Due to friction between brick and rough surface
A body is suspended from a spring hanging vertically. The bodt is then pulled downward so the spring stretches. Consider the change in the elastic potential energy (EPE) of the spring and the change in gravitational potential energy (GPE) as the body is pulled down A.) The GPE decreases while the EPE increases B.) Both the GPE and the EPE decrease C.) The EPE increases but the GPE is unchanged D.) The GPE increases along with the EPE E.) The GPE decreases but with the EPE is unchanged
A.) The GPE decreases while the EPE increases
For a 0.1kg frog to jump to a height of 1.0 meter require an energy of about A.) 10J B). 1.0J C.) 0.5J D.) 0.1J
B). 1.0J The energy = Potential Energy E = PE = MGH = 0.1 * 9.8 * 1 = 0.98 = 1.0J
A child riding on a swing rises to a height of 1.0m above the lowest point. Another child of equal mass whose speed at the lowest point is twice as great will rise A.) To a height which depends on the mass B). Four times as high C.) Twice as high D.) To the same height
B). Four times as high
Work is not being done on an object unless A). Object is being accelerated B). Object is moving C.) Speed is constant D.) Net force on the object is zero
B). Object is moving Work = Force * Displacement
Virgil rides a skateboard (combined mass 100kg) at 4m/s and Jill rides a bicycle (combined mass 64kg) at 5/ms A.) Jill has the greater kinetic energy B). Virgil and Jill have equal kinetic energies C.) Virgil has the greater kinetic energy
B). Virgil and Jill have equal kinetic energies KE = 1/2mv^2 Virgil: 1/2 * 100 * 4^2 = 800J Jill: 1/2 * 64 *5^2 = 800J
Jim exerts a force of 500N against a 100kg desk that does not move. Virgil exerts a force of 400N against a 60kg desk that moves 2m in the direction of the push. Mik exerts a force of 200N against a 50kg desk that moves 4m in the direction of the push. The most work is done by A.) Mik B). Virgil and Mik, who do equal amounts of work C.) Virgil D.) Jim
B). Virgil and Mik, who do equal amounts of work W = F * D Jim Work: 500 * 0 = 0 J Virgil Work: 400 * 2 = 800J Mik Work: 200 * 4 = 800J
Which of the following is not an energy unit A). Energy B). Watt C). kWh D). Joule E). Nm
B). Watt Watt is a unit of power.
Which has the greater kinetic energy - a 1 ton car moving at 30m/s or a half ton car moving at 60ms? A.) A 1 ton car B). A half-ton car C.) both have the same K.E
B). half-ton car KE(1 ton car) = 1/2 * 1000 * 30^2 = 450,000J = 450KJ KE(.5 ton car) = 1/2*500*60^2 = 900,000J = 900J
A child runs at 4.0 m/s and jumps onto a sled intially at rest. If the child's mass is 36kg and if the child and sled slide off together at 3.0 m/s after the collision , the sled's mass is A.) 48kg B.) 12kg C.) 36kg D.) 27kg
B.) 12kg Ptotal Intial = Ptotal Final Pki + PSi = Pksf MkVk +MsVsi = (Mk + Ms) Vf 36 * 4 = ms + 0 = (36 + ms) * 3 144 + 0 = (36 + ms) * 3
Suppose you climb the stairs of a ten story building about 30M high and your mass is 60kg. The gravitational potential energy you gain is about A.) 27000J B.) 18000J C.) 1800J D.) 270J
B.) 18000J PE = MGH = 60 * 9.8 * 30 = 17640 ~ 18000J
Which of the following is not a unit of power A.) Horsepower B.) Kilowatt-Hour C.) Watt D.) Joule/Second E.) Kilowatt
B.) Kilowatt-Hour Kilowatt hour is electrical energy unit
Two people sit face to face on chairs which are free to roll without any friction. They push each other with a force of 50N and move apart. Person A whose mass including the chair is 80kg, moves to the left at 2.5m/s. Person B whose mass including the chair is 50kg A.) Moves to the right at 10 m/s B.) Moves to the right at 4 m/s C.) Moves to the right at 3.16 m/s D.) Moves to the right at 2.5 m/s
B.) Moves to the right at 4 m/s Ptotal(intial) = Ptotal(final) Pai + Pbi = Paf + Pbf 0+0 = 80 * (-2.5) + 50 * vbf 50vbf = 200 vbf = 4m/s to the right
One form of the proper metric unit for for momentum is A.) Kg m B.) N Sec C.) Joule D.) Kg m/s^2
B.) N Sec Force * Time = Momentum Unit Newton * Second
A bowling ball moving to the east at a speed of 1.4 m/s collides head-on with a stationary beach ball of the same diameter but less than one twentieth the mass after the collision the beach ball moves with a speed of 1.6 m/s which of the following is true then? A.) The beach ball has more momentum than the bowling ball B.) The bowling ball has a velocity of slightly under 1.4 m/s to the east C.) The bowling ball and the beach ball have the same momentum after the collision D.) The bowling ball recoils to the west with nearly the same speed as before.
B.) The bowling ball has a velocity of slightly under 1.4 m/s to the east Momentum is conserved.
A quaterback of mass 85kg is running at 10m/s. Also a tackle of mass 100kg is running at 9m/s A.) The tackle has the greater kinetic energy B.) The quarterback has the greater kinetic energy C.) The quarterback and tackle have equal kinetic energies
B.) The quarterback has the greater kinetic energy KE = 1/2mv^2 Q: 1/2 * 85 * 10^2 = 4,250J T: 1/2 * 100 * 9^2 = 4,050J
When work is done by force on an object , then which of the following are true? A.) The object does negative work on the force B.) The work done will be equal to the change of the total energy of the object plus energy appearing as heat, light, sound C.) The energy lost to friction is equal to the amount of work done by the force D.) The mass of the object always increases E.) The speed of object always increases
B.) The work done will be equal to the change of the total energy of the object plus energy appearing as heat, light, sound Work = Change in K.E
Intially, a blue automobile has twice the KE that a red automobile has. Both are braked to a stop; both have the same amount of braking force. The red auto will stop in ____________________ as the blue auto. A.) One fourth the distance B). The same distance C). Half the distance D.) Four times the distance E.) Twice the distance
C). Half the distance
A 5.0kg cat runs to the left at 10m/s and a 10kg dog runs to the right at 5.0m/s. The total kinetic energy is A.) 500J B.) 0 C.) 375J D.) -125J E.) 100J
C.) 375J Energy has no direction then total kinetic energy = KE total KE Total = KE(Cat) + KE(Dog) KE = 1/2mv^2 KE Total = (1/2*5*10^2) + (1/2*10*5^2) = 250 + 125 = 375J
An object with a kinetic energy of 50J is stopped in a distance of 0.01m. The average force that stops the object is A.) 50,000N B). 50N C.) 5,000 N D.) 0.5N E.) 500N
C.) 5,000 N F * D = Change in KE = KE(inital) - KE (final) F * 0.01 = -50 0.01F = - 50 F = 50/0.01 = 5,000N
In attempt to pull a 1500 kg car out of a ditch , Al exerts a force of 200N for 5s, Bill exerts a force of 500N for two s, and Clyde exerts a force of 300N for 4 seconds . The car does not move at all who has the greatest impulse. A.) Al B.) Bill C.) Clyde D.) Al, Bill and Clyde provide equal, indeed zero, impulse.
C.) Clyde Impulse = Force * Time Al: 200 * 5 = 1000Ns Bill: 500 * 2 = 1000Ns Clyde: 300 * 4 = 1200Ns
A box is pushed eastward across a rough horizontal floor by a force acting parallel to the floor. A force providing an impulse directed westward on the body. A.) Gravity B.) Normal reaction for of the floor upward on the body C.) Friction D.) The applied force E.) The fictious force
C.) Friction Rough Surface => Friction; which opposes direction of motion.
A box is pushed across a rough horizontal floor by a force acting parallel to the floor in the direction of motion. A force doing no work during the motion is A.) The applied force B.) Friction C.) Gravity
C.) Gravity The box is not moving in the vertical direction
Which of the following mathematical expressions should be used to calculate the momentum of an auto? A.) Weight x Speed B). Weight x Force C.) Mass x Velocity D.) Mass x Acceleration?
C.) Mass x Velocity P= Mv
A refrigerator weighing 1500N is to be lifted onto a truck bed that is 1.0m above the ground. When pushed up a slanting ramp 2.0m in the length a force of only 800N is required to move it at constant velocity. Comparing the work involved in lifting the fridge straight up to the work in pushing it along the ramp, there is A.) An equal amount of work is required in each case B.) Less work required when the ramp is employed C.) More work required when the ramp is employed
C.) More work required when the ramp is employed Work = Force * Distance Straight Up = 1500 * 1 = 1500J Ramp = 800 * 2 = 1600J
A ping pong ball is dropped vertically onto a stationary bowling ball resting on the floor. Which of the balls experiences the greater force as a result of the collision A.) The ping pong ball B.) The bowling ball C.) Neither, both experience forces of the same size D.) It is impossible to tell from this data.
C.) Neither, both experience forces of the same size Newton's 3RD Law
Suppose you are out on a frozen lake , where there is no friction. Which one of the following would start you moving towards the shore? A.) Shouting at someone on the shore B.) None of these would work C.) Removing a shoe and throwing it away from shore D.) Removing a shoe and throwing it to shore.
C.) Removing a shoe and throwing it away from shore
A grandfather clock that is regulated by a pendulum is taken to the Moon where the acceleration of the gravity is less. Compared to an indentical clock on earth the grandfather clock on the moon will A.) Keep time at the same rate B.) Run fast C.) Run slow
C.) Run slow MGH = 1/2mv^2 G on the moon less than G on Earth PE Moon < PE Earth KE Moon < KE Earth
The power of an engine is the measure of A.) It's ability to outperform a horse B). The total amount of work it can preform C.) The rate at which it can preform work D.) It's volume
C.) The rate at which it can preform work Power = Work/Time
A tennis ball bounces off a brick wall. Which of the following is true? A.) The momentum of the ball is conserved in this process B.) If the collision is elastic , then the ball's velocity does not change in this process C.) The total momentum of the ball, wall and earth is conserved in the process D.) None of these are true
C.) The total momentum of the ball, wall and earth is conserved in the process Total momentum is conserved in any collision
A 5.0kg cat travels to the left at 10m/s and a 10kg dog travels to the right at 5.0m/s. The total momentum is A.) 100kg m/s to the right B.) 125kg m/s to the left C.) 50kg m/s to the right D.) Zero
D.) Zero Momentum is a vector.
A box is moved 10 m across a smooth floor by a force making a downward angle with the floor so that there is effectively a 10N force acting parallel to the floor in the direction of motion and a 5N force acting perpendicular to the floor. The work done is A.) 5.0J B.) 50J C.) 150J D.) 100J E.) 10J
D.) 100J Work = Force Parallel * Distance W = 10 * 10 = 100J
In a head on automobile collision, a person's momentum could be reduced from 2,000 kg m/s to zero in just 0.1 s. If this occurs, the average force exerted to stop the person is A.) Can't answer the question without knowing person's mass B.) 200 N C.) 2,000N D.) 20,000N
D.) 20,000N Impulse = Change in momentum F * T = Pf - Pi F * I = 0 - 2000N F = -2000N
A 20N ball and a 40N ball are dropped at the same time from a height of 10M. Air resistance is negligible. Which of the following statements are accurate. A.) The heavy ball has a greater acceleration and falls faster B.) The light ball has a greater speed since it can accelerate faster than the heavy ball C.) After 1 second has elapsed, both balls have the same kinetic energy since they have the same acceleration D.) Both balls hit the ground at the same time but gravity does more work on the heavy ball than on the light ball.
D.) Both balls hit the ground at the same time but gravity does more work on the heavy ball than on the light ball. More Mass = More Energy
The momentum of a truck is increased by a factor of 4. It's weight does not change, thus A.) It's acceleration doubled B.) It's kinetic energy doubled C.) It's speed doubled D.) It's speed increased by a factor of 4
D.) It's speed increased by a factor of 4
A ball at the end of a string is swinging as a simple pendulum. Assuming no loss in energy due to the friction we can say for the ball that A.) The potential energy is maximum where the kinetic energy is maximum B.) The kinetic energy is maximum at each end of the motion C.) The potential energy is maximum at the lowest position of the ball D.) The potential energy is maximum where the kinetic energy is a minimum
D.) The potential energy is maximum where the kinetic energy is a minimum
A quantity which is conserved in the collision of a car and a truck is? A.) Nervous energy B). Momentum of the truck C.) Momentum of the car D.) Total Momentum E.) Kinetic Energy
D.) Total Momentum As general collision => Conservation of momentum inelastic or elastic collision.
The potential energy of a spring of constant K that has been stretched to a distance x is given by A.) (1/2)k/x B). (1/2)kx C.) kx D.) kx^2 E.) (1/2)kx^2
E.) (1/2)kx^2 PE= (1/2)kx^2
A block sits on a slight incline, held at rest by the frictional force between the block and the incline. Which of the following statements is true? A.) The frictional force preforms no work since there is no motion of the block B.) The work done by gravity is entirely converted into heat because of the friction present C.) None of these are true D.) The work done by the frictional force is negative since the force of friction opposes the direction of the block is being tugged by gravity E.) The work by the frictional force is equal to the gravitational potential energy of the block
E.) The work by the frictional force is equal to the gravitational potential energy of the block
