scnc 205 midterm ch 4
Two billiard balls having the same mass roll toward each other, each moving at the same speed. What is the combined momentum of the two balls?
0 kg ∙ m/s
A 30-kg girl and a 25-kg boy face each other on friction-free roller blades. The girl pushes the boy, who moves away at a speed of 1.0 m/s. The girl's speed is
0.83 m/s.
If you exert 1 N for a distance of 1 m in 1 s, you will deliver a power of
1 W
It takes 40 J to push a large box 4 m across a floor. Assuming the push is in the same direction as the move, what is the magnitude of the force on the box?
10 N
A machine puts out 100 W of power for every 1000 W put into it. The efficiency of the machine is
10 percent
A person on the edge of a roof throws a ball downward. It strikes the ground with 100 J of kinetic energy. The person throws an identical ball upward with the same initial speed, and this too falls to the ground. Neglecting air resistance, the second ball hits the ground with a kinetic energy of
100 J
A 2-kg mass has 40 J of potential energy with respect to the ground. Approximately how far is it located above the ground?
2 m
Consider a hydraulic press. When the input piston is depressed 20 cm, the output piston is observed to move 1 cm. On the same press, an input force of 1 N can raise no more than
20 N
A 1000-kg car moving at 10 m/s brakes to a stop in 5 s. The average braking force is
2000 N
A 4-kg ball has a momentum of 12 kg ∙ m/s. What is the ball's speed?
3 m/s
A TV set is pushed a distance of 2 m with a force of 20 N that is in the same direction as the set moves. How much work is done on the set?
40 J
A bow is drawn so that it has 40 J of potential energy. When fired, the arrow will ideally have a kinetic energy of
40 J
Using 1000 J of work, a toy elevator is raised from the ground floor to the second floor in 20 s. How much power does the elevator use?
50 W
A jack system will increase the potential energy of a heavy load by no more than 1000 J with a work input of 2000 J. The efficiency of the jack system is no more than
50 percent.
The average momentum of a 70-kg runner who covers 400 m in 50 s is
560 kg ∙ m/s.
A 2-kg mass is held 4 m above the ground. What is the approximate potential energy of the mass with respect to the ground?
80 J
Which requires more work: lifting a 50-kg sack vertically 2 m or lifting a 25-kg sack vertically 4 m?
Both require the same amount of work.
The conservation of momentum is most closely related to
Newton's Third Law.
Which of the following has the largest momentum relative to the earth?
a pickup truck speeding along a highway
A feather and a coin dropped in a vacuum fall with equal
accelerations.
A car traveling along the highway needs a certain amount of force exerted on it to stop. More stopping force may be required when the car has
all of the above
A heavy pile driver starting from rest falls on a pile with a force that depends on the
all of the above
A heavy truck and a small car rolling down a hill at the same speed are forced to stop in the same amount of time. Compared to the force that stops the car, the force needed to stop the truck is
all of the above
You're driving down the highway and a bug spatters on your windshield. Which undergoes the greater change in momentum?
both the same
When you jump from an elevated position, you usually bend your knees upon reaching the ground. By doing this, the time of the impact is about ten times more than for a stiff-legged landing. In this way, the average force your body experiences is reduced by
bout ten times.
When a rifle is fired, it recoils so both the bullet and rifle are set in motion. The rifle and bullet ideally acquire equal
but opposite amounts of momentum
A cannon recoils from firing a cannonball. The speed of the cannon's recoil is small because the
cannon has more mass than the ball.
Momentum is transferred to the ground when an apple falls on it. The momentum absorbed by the ground is
greater than that of the apple only if the apple bounces.
A clerk can lift containers a vertical distance of 1 m or can roll them up a 2-m-long ramp to the same elevation. With the ramp, the applied force required is about
half as much
A bullet is fired from a gun. The speed of the bullet will be about the same as the speed of the recoiling gun
if the mass of the bullet equals the mass of the gun.
A cannonball shot from a cannon with a long barrel will have a greater muzzle velocity because the cannonball receives a great
impulse
According to the impulse-momentum equation Ft = change in (mv), a bungee jumper in fall has momentum which is reduced by the force F exerted by the bungee cord. If m is the mass of the jumper, then v in the equation is the speed of the
jumper.
Compared with falling on a wooden floor, a wine glass may not break when it falls to a carpeted floor because of the
longer time to stop.
A moving object on which no forces are acting will continue to move with constant
momentum
Two objects, A and B, have the same size and shape, but A is twice as heavy as B. When they are dropped simultaneously from a tower, they reach the ground at the same time, but A has greater
momentum
What does an object have when moving that it doesn't have when at rest?
momentum
An object that has kinetic energy must be
moving
If you push for an hour against a stationary wall, no work is done
on the wall.
A job is done slowly, while an identical job is done quickly. Both jobs require the same amount of work, but different amounts of
power.
Which has greater kinetic energy, a car traveling at 30 km/h or a car of half that mass traveling at 60 km/h?
the 60-km/h car
It is correct to say that impulse is equal to
the change in momentum
If you push an object with twice the work input for twice the time, your power input is
the same amount as for half the work in half the time.
A 50-kg sack is lifted 2 m in the same time as a 25-kg sack is lifted 4 m. The power expended in raising the 50-kg sack compared to the power used to lift the 25-kg sack is
the same.
Suppose a gun were made of a strong but very light material. Suppose also that the pellet is more massive than the gun itself. For such a weapon
the target would be safer than the shooter.
The difference between impulse and impact force involves the
time the force acts
Two identical arrows, one with twice the kinetic energy of the other, are fired into a hay bale. The faster arrow will penetrate
twice as far as the slower arrow.
An object is raised above the ground gaining a certain amount of potential energy. If the same object is raised twice as high, it gains
twice as much potential energy
A 1000-kg car and a 2000-kg car are hoisted the same distance in a gas station. Raising the more massive car requires
twice as much work.
When an object is lifted 10 m, it gains a certain amount of potential energy. If the same object is lifted 20 m, its potential energy gain is
twice as much.
A bungee jumper makes her jump. The force of the bungee cord on her is greatest when her
velocity is minimum.
Recoil is noticeable if we throw a heavy ball while standing on roller skates. If instead we go through the motions of throwing the ball but hold onto it, our net recoil will be
zero
The force that accelerates a rocket in outer space is exerted on the rocket by the
exhaust gases.
A woman lifts a box from the floor. She then moves with constant speed to the other side of the room, where she puts the box down. How much work does she do on the box while walking across the floor at constant speed?
0 J
A ball is moving at 4 m/s and has a momentum of 48 kg ∙ m/s. What is the ball's mass?
12 kg
A car moves four times as fast as an identical car. Compared to the slower car, the faster car has
16 times the KE.
If you exert 100 J in 50 s, your power output is
2 W
An object that has potential energy may have this energy because of its
location.
When you are in the way of a fast-moving object and can't get out of its way, you will suffer a smaller force of impact if you decrease its momentum over a
long time.
If you do work on an object in half the time, your power output is
twice the usual power output.
A piece of putty moving with 1 unit of momentum strikes and sticks to a heavy bowling ball that is initially at rest. After the putty sticks to the ball, both move with a combined momentum of
1 unit.
A karate expert executes a swift blow and severs a cement block in two with her bare hand. The magnitude is the same for the
all of the above
A moving object has
all of the above
The force on an apple hitting the ground depends upon
all of the above
Strictly speaking, if any electrical device in your car is turned on (such as an air conditioner, headlights, or even a radio), more gasoline is burned by the engine. This statement is
always true
Bullets are fired from an airplane in the forward direction of motion. The momentum of the airplane will be
decreased
Whereas impulse involves the time that a force acts, work involves the
distance that a force acts.
A freight train rolls along a track with considerable momentum. If it rolls at the same speed but has twice as much mass, its momentum is
doubled.
An ungloved fist will do more damage to a jaw than a gloved fist. The reason for this is that the ungloved fist
exerts a larger force on the jaw.
When a car is braked to a stop, its kinetic energy is transformed to
heat.
A heavy truck and a small truck roll down a hill. Neglecting friction, at the bottom of the hill, the heavy truck will have greater
momentum.
If an object has kinetic energy, then it also must have
momentum.
The average force that a bungee cord exerts on a jumper, multiplied by the time of stretch, equals the jumper's change in
momentum.
In order to catch a ball, a baseball player extends the hand forward before impact with the ball and then lets it ride backward in the direction of the ball's motion upon impact. Doing this reduces the force of impact on the player's hand principally because the
time of impact is increased.
If you push an object just as far while applying twice the force, you do
twice as much work.
If you push an object twice as far while applying the same force, you do
twice as much work.
One end of a long uniform log is raised to shoulder level. An identical log is raised at its center to the same level. Raising the second log requires about
twice as much work.
