Physics Multiple Choice 3
A 0.20 kg rubber ball is dropped from the window of a building. It strikes the sidewalk below at 30m/s and rebounds 20 m/s. The change in momentum of the ball as a result of the collision with the sidewalk is:
10 kgm/s ∆P=.20(20-(-30))
A 2.5kg stone is released from rest and falls toward the Earth. After 4s, its momentum is:
100 kgm/s Vf-Vi=at P=mV
A 5kg cart is moving horizontally at 6m/s. In order to change its speed to 10m/s the net work done on the cart must be:
160J W=∆E W=½m(Vf²-Vi²)
A 2kg object is moving at 3m/s. A 4N force is applied in the direction of motion and then removed after object has traveled an additional 5m. The work done by this force is:
20J W=Fxcosθ = (4)(5)(1)
Bullets from two revolvers are fired with the same velocity. The bullet from gun#1 is twice as heavy as the bullet from gun #2. Gun #1 weighs three times as much as gun #2. The ration of the momentum imparted to gun #1 to that imparted to gun #2 is:
2:1 2mV=mV, mass of guns don't affect momentum, only input
A 1.0kg ball moving at 2 m/s perpendicular to a wall rebounds from the wall at 1.5m/s. The change in the momentum of the ball is:
3.5Ns away from the wall ∆P=m(Vf-Vi)
An elevator is rising at constant speed. Consider the following statements: I. the upwards cable force is constant II. the kinetic energy of the elevator is constant III. the gravitational potential energy of the Earth-elevaotr system is constant IV. the acceleration of the elevator is zero V. the mechanical energy of the Earth-elevator system is constant
I, II, and IV
Momentum may be expressed in:
Ns
A cart loaded with sand slides along a horizontal frictionless track. As the cart moves, sand trickles out at a constant through a hole in the back of the cart. The speed of the cart will:
Remain the same because the sand is falling vertically
Two bodies of unequal mass, placed at rest on a frictionless surface, are acted on by equal horizontal forces for equal times. Just after these forces are moved, the body of greater mass will have: a. the greater speed b. the greater acceleration c. the smaller momentum d. the greater momentum e. the same momentum as the other body
e. the same momentum as the other body
The velocity of a particle moving along the x axis changes from vi to vf. For which values of vi and vf is the total work done on the particle negative? a. vi=2m/s, vf=5m/s b. vi=-2m/s, vf=5m/s c. vi=-2m/s, vf=-5m/s d. vi=2m/s, vf=-5m/s e. vi=-5m/s, vf=2m/s
e. vi=-5m/s, vf=2m/s 2²-(-5)²=-21
A block is attached to the end of an ideal spring and moved from coordinate xi to xf. The relaxed position is x=0. The work done by spring is positive if: a. xi=2 and xf=4 b. xi=-2 and xf=4 c. xi=-2 and xf=-4 d. xi=2 and xf=-4 e. xi=-4 and xf=-2
e. xi=-4 and xf=-2 Ws=-∆Us Ws=-(kxf²-kxi²)=-(4-16)=12
A watt×second is a unit of:
energy
A Boston Red Sox baseball player catches a ball of mass m that is moving toward him with speed v. While bringing the ball to rest, his hand moves back a distance of d. Assuming constant deceleration, the horizontal force exerted on the ball by his hand is:
mV²/2d W=∆KE Fd= 0 - ½mV² F=mV²/2d
A woman lifts a barbell 2m in 5s. If she lifts is the same distance in 10s, the work done by her is:
the same
A rifle of mass M is initially at rest but free to recoil. It fires a bullet of mass m and velocity v. After firing, the velocity of the rifle is:
-mv/M=Vf mvi+MV=mVf+Mv
Two objects with masses, m1 and m2, have the same kinetic energy and are both moving to the right. The same constant force F is applied to the left to both masses. If m₁=4m₂, the ratio of the stopping distance of m1 to that of m2 is:
...
An object of mass 1g is whirled in a horizontal circle of radius 0.5m at a constant speed of 2m/s. The work done on the object during one revolution is:
0
boy holds a 40N weight at arm's length for 10s. His arms are 1.5m above the ground. The work down by the force of the boy on the weight while he is holding it is:
0
A 64 kg woman stands on frictionless level ice. She kicks a 0.10kg stone backwards with her foot so that the stone acquires a velocity of 1.1m/s. The velocity she acquired is:
0.0017 forward b/c of conservation of momentum
Sphere X, of mass 2kg, is moving to the right at 10m/s. Sphere Y, of mass 4kg, is moving to the left at 10m/s. The two spheres collide head-on. The ratio of the magnitude of the impulse exerted by X on Y to that exerted Y on X is:
1 because equal and opposite reactions- Newton's 3rd Law
Camping equipment weighing 6000N is pulled across a frozen lake by means of a horizontal rope. The coefficient of kinetic friction is 0.05. How much work is done by the campers in pulling the equipment 1000m is its speed is decreasing at the constant rate of 0.20m/s²?
1.8×10⁵J
The weight of an object on the moon is 1/6 of its weight on earth. THe ratio of the kinetic energy of a body on the earth moving with speed V to that of the same body moving with speed V on the moon is:
1:1 because mass is constant
A sledge weighs 5000N. It is pulled on level snow by a dog team exerting a horizontal force on it. The coefficient of kinetic friction between sledge and snow is 0.05. How much work is done by the dog team pulling the sledge 1000m at constant speed?
2.5×10⁵J Ff=µmg W=µmgx
An ideal spring is used to fire a 15.0g block horizontally across a frictionless table top. The spring's k is 20N/m and is initially compressed by 7cm. The speed of the block as it leaves the spring is:
2.6m/s Us=KE
A man pushes an 80N crate a distance of 5m upward along a frictionless slope that makes an angles of 30⁰ with the horizontal. The force he exerts is parallel to the slope. If the speed of the crate is constant, then the work done by the man is:
200J W=∆Ug=(80)(25)-(80)(0)
Camping equipment weighing 6000N is pulled across a frozen lake by means of a horizontal rope. The coefficient of kinetic friction is 0.05. The work done by the campers in pulling the equipment 1000m at constant velocity is:
3×10⁵J
Two trailers, X with mass 500kg and Y with mass 2000kg, are being pulled at the same speed. The ratio of the kinetic energy of Y to that of X is:
4:1 ½mV²=½mV² ½(500)V²=½(2000)V²
An object is constrained by a cord to move in a circular path of radius 0.5m on the a horizontal frictionless surface. The cord will break if tension exceeds 16N. The maximum kinetic energy of the object is:
4J 16=mV²/r KE=mV²
A 8000N car is traveling at 12m/s along a horizontal road when the brakes are applied. The car skids to a stop in 4s. How much kinetic energy does the car lose in this time?
5.9×10⁴J ½mV²
An ideal spring, with a pointer attached to its end, hangs next to a scale. With a 100N weight attached, the pointer indicates 40 on the scale. Using a 200N weight instead results in 60 on the scale. Using an unknown weight X instead results in 30 on the scale. The weight of X is:
50N
A 0.5kg block sides along a horizontal frictionless surface at 2m/s. It is brought to rest by compressing a very long spring of spring constant 800N/m. The maximum spring compression is:
5cm KE=Us
Suppose that the fundamental dimensions are taken to be: force F, velocity V, and time T. The dimensions of potential energy are then:
FVT
A man pulls a sled along a rough horizontal surface by applying a constant force F at an angle θ above the horizontal. In pulling the sled a horizontal distance d, the work done by the man is:
Fdcosθ
An object moves in a circle at constant speed. The work done by the centripetal force is zero because: a. The displacement for each revolution is 0 b. the av. force for each revolution is 0 c. there is no friction d. the magnitude of the acceleration is 0 e. the centripetal force is perpendicular to the velocity
a. The displacement for each revolution is 0
The momentum of an object at a given instant is independent of its: a. inertia b. mass c. speed d. velocity e. acceleration
acceleration
Which of the following groups does not contain a scalar quantity? a. velocity, force, power b. displacement, acceleration, force c. acceleration, speed, work d. energy, work, distance e. pressure, weight, ti e
b. displacement, acceleration, force
The amount of work required to stop a moving object is equal to the: a. velocity of the object b. kinetic energy of the object c. mass of object × acceleration d. mass of object × velocity e. square of the velocity of the object
b. kinetic energy of the object
Which of the following five objects requires the greatest change in momentum to stop moving? a. object= electron, mass= 10⁻³⁰, speed= 10⁷m/s b. object= oil tanker , mass= 10⁸, speed= 10⁻¹ c. object= rain drop, mass=10⁻⁴, speed= 10m/s d. object=snail, mass=10⁻², speed=10⁻⁴ e. object=satellite, mass=10kg, speed=10⁴
b. object= oil tanker , mass= 10⁸, speed= 10⁻¹ ∆P=m(-Vi)
A 10kg block of ice is at rest on a frictionless horizontal surface. A 1N force is applied in an easterly direction for 1s. During this time interval, the block: a. acquires a speed of 1m/s b. moves 10 cm c. acquires a momentum of 1.0 kg m/s d. acquires a kinetic energy of 0.1J e. none of the above
c. acquires a momentum of 1.0 kg m/s
Which of the following bodies has the largest kinetic energy? a. mass 3M, speed V b. mass 3M, speed 2V c. mass 2M, speed 3V d. mass M, speed 4V e. all four have the same kinetic energy
c. mass 2M, speed 3V
Two objects interact with each other and with no other objects. Initially object A has a speed of 5m/s and object B has a speed of 10 m/s. In the course of their motion they return to their initial positions. Then A has a speed of 4m/s and B has a speed of 7m/s. We can conclude that: a. the potential energy changed from the beginning to the end of the trip b. mechanical energy was increased by nonconsecutive forces c. mechanical energy was decreased by nonconsecutive forces d. mechanical energy was increased by consecutive forces e. mechanical energy was decreased by consecutive forces
c. mechanical energy was decreased by nonconsecutive forces
If two different masses have the same kinetic energy, their momenta are: a. proportional to their masses b. proportional to the square of their masses c. proportional to the square roots of their masses d. inversely proportional to their masses e. inversely proportional to the square roots of their masses
c. proportional to the square roots of their masses
A body at rest is capable of doing work if: a. the potential energy is positive b. the potential energy is negative c. is is free to move in such a way as to decrease its kinetic energy d. is is free to move in such a way as to decrease its potential energy e. is is free to move in such a way as to increase its potential energy
d. is is free to move in such a way as to decrease its potential energy
A force acting on a particle is conservative is: a. its work equals the change in kinetic energy of the particle b. it obeys Newton'd 2nd law c. it obeys Newton'd 3rd law d. its work depends on the end points of the motion, not the path between e. it is not a frictional force
d. its work depends on the end points of the motion, not the path between
Which of the following five quantities is NOT an expression for energy? Here m is a mass, g is the acceleration due to gravity, h and d are distance, F is a force, v is a speed, a is acceleration, P is power, and t is time. a. mgh b. Fd c. 1/mV² d. ma e. Pt
d. ma F=ma
A ball is thrown into the air. As it rises there is an increase in its: a. acceleration b. velocity c. kinetic energy d. potential energy e. momentum
d. potential energy
The law of conservation of momentum applies to a system of colliding objects only if: a. there is no change in kinetic energy of the system b. the coefficient of restitution is one c. the coefficient of restitution is 0 d. the net external impulse is 0 e. the collisions are all elastic
d. the net external impulse is 0
A nonconsecutive force: a. violates Newton's 2nd law b. violates Newton's 3rd law c. cannot do any work d. must be perpendicular to the velocity of the particle on which it acts e. none of the above
e. none of the above laws cannot be violated friction does work
A student's life was saved in an automobile accident because an airbag expanded in front of his head. If the car had not been equipped with an airbag, the windshield would have stopped the motion of his head in a much shorter time. Compared to the windshield, the airbag:
exerts a much smaller force over a greater time
In raising an object to a given height by means of an inclined plane, as compared with raising the object vertically, there is a reduction in:
force required
A 8N block slides down an incline. It has an initial speed of 7m/s. The work done by the resultant force on this block is:
impossible to calculate without more information
A golf ball of mass m is hit by a golf club so that the ball leaves the tee with speed v. The club is in contact with the ball for time T. The average force on the club on the ball during the time T is:
mv/t P=F∆T F/t=mV
A baseball is hit high into the upper bleachers of left field. OVer its entire flight the work done by gravity and the work done by air resistance, respectively, are:
negative; negative
A person holds a 80N weight 2m above the floor for 30s. The power required to do this is:
none of these. 0
The work done by gravity during the descent of a projectile is:
positive
A man, standing at rest on a horizontal frictionless floor, might get himself moving by:
throwing his shoe horizontally
For a block of mass m to slide without friction up the rise of height h shown, it must have a minimum initial sped of:
√2gh V²=2gh
