P199 Homework 3
Imagine you're in a completely dark room with no windows and you cut a 1-ft^2 round hole in the roof. When the Sun is high in the sky, about 100 W of solar power enters the hole. On the floor where the light hits, you place a beach ball covered with aluminum foil, with the shiny side out. Discuss the illumination in your room compared with that of a 100-W incandescent lightbulb?
Illumination by each would be much the same, 100 W.
A lunar vehicle is tested on Earth at a speed of 12 km/h. When it travels at the same speed on the Moon, is its momentum greater, less, or the same?
Its momentum is the same.
Find the kinetic energy of an 78-kg scooter moving at 2.0 m/s . (1J is equivalent to 1N⋅m, which is equivalent to 1kg⋅m2/s^2.).
K = 160 J
A sustained force of 58 N moves a model airplane 30 m along its runway to provide the required speed for takeoff. Find the kinetic energy at takeoff.
K = 1700 J
The impulse-momentum relationship is a direct result of
Newton's second law.
The conservation of momentum is closely related to
Newton's third law.
A 1-N apple falls to the ground. The apple hits the ground with a force of
Not enough information.
Suppose an astronaut in outer space plays a solitary game of "throw, bounce, and catch" by tossing a ball against a very massive and perfectly elastic concrete wall.
The astronaut will never catch the first bounce.
If an object's kinetic energy is zero, what is its momentum?
The momentum is zero.
Find what work is done when a 24-N force moves a cart 3.5 m from its initial position. (1J=N⋅m).
W = 84 J
Which of the following has the largest momentum relative to Earth?
a pickup truck speeding along a highway
When you jump from an elevated position you usually bend your knees upon reaching the ground. By doing this, the contact time is about 10 times more than for a stiff-legged landing and the average force your body experiences is reduced by
about 10 times.
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.
An open freight car rolls friction-free along a horizontal track in vertically pouring rain. As water accumulates in the car, its speed
decreases.
Freddy Frog drops vertically from a tree onto a horizontally-moving skateboard. Immediately after landing on the skateboard, Freddy's speed
decreases.
When bullets are fired from an airplane in the forward direction of motion, the momentum of the airplane
decreases.
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.
The force that accelerates a rocket in outer space is exerted on the rocket by the
exhaust gases.
A hydraulic press properly arranged, like a simple lever, is capable of multiplying energy input.
false.
A car that travels twice as fast as another car when braking to a stop will skid
four times as far.
You use a straw for a pea shooter. The speed of the pea emerging from the straw when you blow through it will be greater if the straw is
full length.
When an apple falls to the ground, momentum is transferred to the ground. The momentum absorbed by the ground is
greater than that of the apple if the apple bounces.
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 with the force to stop the car, the force needed to stop the truck is
greater.
A clerk can lift containers a vertical distance of 1 m, or roll them up a 2-m-long ramp to the same elevation. With the ramp, the applied force needed is
half as much.
When a non-hybrid car brakes to a stop its kinetic energy transforms to
heat.
The speed of a bullet fired from a gun will be about the same as the speed of the recoiling gun
if the masses of the bullet and gun are equal.
A cannonball fired from a long-barrel cannon will have a greater muzzle velocity because the cannonball receives a greater
impulse.
According to the impulsemomentum 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 to a recoiling rifle, the bullet that is fired has a greater
kinetic energy.
If a charging rhinoceros has momentum, it must also have
kinetic energy.
A ball is projected into the air with 900 J of kinetic energy that is transformed to potential energy at the top of its trajectory. When it returns to its original level after encountering air resistance, its kinetic energy is
less than 900 J.
An object may have potential energy because of its
location.
When you are in the way of a fast-moving object and can't get escape, you will suffer a smaller force if the collision time is
long.
Compared with falling on a wooden floor, a wine glass may not break when it falls on a carpeted floor because of
longer time to stop.
When a cannon fires a cannonball at a given speed, the smaller recoil speed of the cannon is due to different
masses.
A golf ball is thrown at and bounces backward from a massive bowling ball that is initially at rest. After the collision, compared to the golf ball, the bowling ball has more
momentum, but less kinetic energy.
A heavy truck and a small truck roll down a hill. Neglecting friction, at the bottom of the hill the heavy truck has greater
momentum.
A 1-kg ball dropped from a height of 2 m rebounds only 1.5 m after hitting the ground. The amount of energy converted to heat is about
more than 2.0 J.
A boulder is dropped onto mud and plows into it a certain distance. If it hits with three times as much speed, the distance it plows into the mud will likely be
more than three times as deep.
A dog and a mouse run along a road with the same kinetic energy. The faster runner is the
mouse.
An object that has kinetic energy must be
moving.
If you push for an hour against a stationary wall, you do no work
on the wall.
Suppose a gun were made of strong lightweight material with a pellet that is more massive than the gun. Then firing speed is greater for the
recoiling gun.
From the same height you simultaneously drop a lightweight tennis ball and a heavyweight bowling ball. When they hit the floor they have the same
speed.
Which has greater kinetic energy, a car traveling at 30 km/h or another car of half the 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.
No work is done by gravity on a bowling ball that rolls along a bowling alley because
the force on the ball is at right angles to the ball's motion.
A baseball and a golf ball have the same momentum. Which has the greater kinetic energy?
the golf ball
Consider driving into a massive concrete wall with no "give," versus having a head-on collision at the same speed with an identical car moving toward you at the same speed. It would be more damaging to hit the
the same for both.
In order to catch a fast-moving softball with your bare hand, you extend your hand forward just before the catch and then let the ball ride backward with your hand. Doing this reduces the catching force because the
time of catch is increased.
The distinction between impulse and force involves the
time the force acts.
Strictly speaking, if any electrical device in an automobile is turned on (such as an air conditioner, headlights, or radio), more fuel is consumed by the engine. This statement is
true.
A 1000-kg car and a 2000-kg car are hoisted the same distance in a service station. Raising the more massive car requires
twice as much work.
If you push an object twice as far while applying the same force, you do
twice as much work.
When you push an object a certain distance while applying twice the force, you do
twice as much work.
An object lifted 10 m gains a certain amount of potential energy. If it is lifted 20 m, its gain in potential energy is
twice as much.
If you do work on an object in half the time, your power output is
twice.
A sandbag in outer space moves at 3 m/s when it collides and sticks to a half-as-massive sandbag initially at rest. Compared with the kinetic energy of the moving sandbag before collision, the kinetic energy of the coupled sandbags after collision is
two-thirds.
Recoil is noticeable if we throw a heavy ball while standing on a skateboard. If instead we go through the throwing motion but hold onto the ball, without friction effects our net recoil will be
zero.
Find the momentum change of the cart when an average force of 27 N exerted on a cart for 2.6 s .
Δp = 70 kg⋅m/s
A moving object has
-energy. -velocity. -speed. -momentum.
A car traveling along the highway needs a certain amount of braking force to stop. More braking force is required when the car
-has the same momentum but must stop in a shorter distance. -has more mass but has the same speed and must stop in the same distance. -has more momentum but must stop in the same distance.
The massive ram of a pile driver falling from rest strikes a pile with a speed that depends on the
-initial potential energy of the ram. -distance the ram falls. -initial height of the ram.
The force of a falling apple hitting the ground depends upon
-the speed of the apple just before it hits. -whether or not the apple bounces. -the time of contact with the ground.
A karate expert executes a swift blow and severs a brick with her bare hand. Equal magnitudes occur for the
-time of contact on both the block and the expert's hand. -force on both the brick and the expert's hand. -impulse on both the brick and the expert's hand.
Two billiard balls having the same mass roll toward each other at the same speed. What is the net momentum of the two-ball system?
0 kg•m/s.
Two identical freight cars roll without friction towards each other on a level track. One car rolls at 2 m/s and the other car rolls at 1 m/s. After the cars collide, they couple and roll together with a speed of
0.5 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.
Exert 1 N for a distance of 1 m in 1 s and you deliver a power of
1 W.
A 1-kg chunk of putty moving at 1 m/s collides and sticks to a 5-kg bowling ball initially at rest. The bowling ball and putty move with a momentum of
1 kg•m/s.
A rifle of mass 2 kg is horizontally suspended by a pair of strings so that recoil can be measured. The rifle fires a bullet of mass 1/100 kg at a speed of 200 m/s. The recoil velocity of the rifle is about
1 m/s.
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.
Two identical gliders slide toward each other on an air track. One glider moves at 1 m/s and the other glider moves at 2 m/s. They collide and stick. The combined gliders move at
1/2 m/s.
A 5-kg fish swimming at a speed of 1 m/s swallows an absent-minded 1-kg fish swimming toward it at 4 m/s. The speed of the larger fish after lunch is
1/6 m/s.
Consider gliders that slide friction-free along a horizontal air track. Glider A has a mass of 1 kg, a speed of 1 m/s, and collides with glider B, which has a mass of 5 kg and is at rest. If they stick upon collision the speed the combined gliders will be
1/6 m/s.
It takes 40 J to push a large crate 4 m across a floor. The force exerted on the crate is
10 N.
A person on the edge of a roof throws a piece of tile downward that strikes the ground with 100 J of kinetic energy. Another identical tile is thrown upward with the same initial speed, and this too falls to the ground. Neglecting air resistance, the second tile hits the ground with a kinetic energy of
100 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 4 times as fast as another identical car. Compared with the slower car, the faster car has
16 times the kinetic energy.
A 2-kg mass that weighs 20 N has 40 J of potential energy relative to the ground. What is its height?
2 m.
When the input piston of a hydraulic press is depressed 20 cm, the output piston is observed to move 1 cm. An input force of 1 N can raise no more than
20 N.
A 1000-kg car moving at 10 m/s that brakes to a stop in 5 s has an average braking force of
2000 N.
A 4-kg ball has a momentum of 12 kg•m/s. What is the ball's speed?
3 m/s
A bow is drawn so that it has 40 J of potential energy. When the arrow is fired its kinetic energy is ideally
40 J.
A music console is pushed a distance of 2 m with a force of 20 N. The work done on the console is
40 J.
A 5-kg fish swimming at a speed of 1 m/s swallows an absent-minded 1-kg fish at rest. The speed of the larger fish after lunch is
5/6 m/s.
A piece of taffy slams into and sticks to another identical piece of taffy that is at rest. The momentum of the two pieces of taffy stuck together after the collision is the same as it was before the collision. Kinetic energy is a different story, for part of it turns into heat. What percentage of the kinetic energy converts into heat?
50%.
In raising a 5000-N piano with a pulley system, for every 1 m of rope pulled down, the piano rises 0.1 m. Ideally, this means the force needed to lift the piano is
500 N.
A diver who weighs 500 N steps off a diving board 10 m above the water hits the water with kinetic energy of
5000 J
A 5000-kg freight car crashes into a 10,000-kg freight car at rest. They couple upon collision and move with a speed of 2 m/s. What was the initial speed of the 5000-kg freight car?
6 m/s.
A sandbag is motionless in outer space. A second sandbag with 3 times the mass moving at 12 m/s collides with it and they both stick together and move at a speed of
6 m/s. 8 m/s. 4 m/s. 3 m/s. **none of the above**
A boxer punches a sheet of paper in midair from rest to a speed of 40 m/s in 0.05 s. If the mass of the paper is 0.01 kg, the force of the punch on the paper is
8.0 N.
A 2-kg mass weighs 20 N and is held 4 m above the ground. Its potential energy relative to the ground is
80 J.
Sam pushes crates starting from rest across the floor of his classroom for 3 s A. 100 N, 30 kg B. 75 N, 20 kg C. 30 N, 10 kg A. For each crate, rank impulses delivered from greatest to least. B. For each crate, rank changes in momentum from greatest to least. C. For each crate, rank final speeds from greatest to least. D. For each crate, rank momenta in 3 s from greatest to least.
A. A is greatest B C is least B. A is greatest B C is least C. C is greatest B A is least D. A is greatest B C is least
A simple lever is used to lift a heavy load. When a 52-N force pushes one end of the lever down 0.90 m , the load rises 0.30 m . A. How much work is done by the 52-N force? B. What is the gain in potential energy of the load? C. How does the work done compare with the increased potential energy of the load?
A. W = 47 J B. ΔU = 47 J C. They are the same.
You're driving down the highway and a lovebug spatters onto your windshield. Which undergoes the greater change in momentum?
Both the same.
You're driving down the highway and a lovebug spatters onto your windshield. Which undergoes the greater force of impact?
Both the same.
You're driving down the highway and a lovebug spatters onto your windshield. Which undergoes the greater impulse?
Both the same.
In the textbook we learned the definition of acceleration, a=Δv/Δt, and we learned that the cause of acceleration involves net force, where a=F/m. Equate these two equations for acceleration and express, for constant mass, FΔt.
FΔt=Δ (mv)
