Physical Science Exam 2

What is it called when we make the momentum come out the same at the end as it was in the beginning of the problem

Conservation of momentum

Consider a block of ice on a friction-free frozen lake. Suppose a continuous force acts on the block. Of course, this causes the block to accelerate. After the force has acted for some time the speed of the block has increased a certain amount. If the force and action time are unchanged, but the mass of the block is doubled, then the speed increase will be...

Cut in half It is twice as hard to move the block, so speed decreases (nothing to do with gravity)

Suppose an open railroad car is rolling without friction in a vertical-falling downpour and an appreciable amount of rain falls into the car and accumulates there. Consider the effect of the accumulating rain on the speed, momentum and kinetic energy of the car. The kinetic energy will....?

Decrease Kinetic energy turns to heat Water in car is warmer than outside water

Consider a block of ice on a friction-free frozen lake. Suppose a continuous force acts on the block. Of course, this causes the block to accelerate. After the force has acted for some time the speed of the block has increased a certain amount. Now if the force and masse of the block are unchanged, but the time the force acts is doubled then the increase in the speed will be...

Doubled

True or False? Kinetic Energy can be conserved

False some of it gets turned into heat

The force exerted on a house by 120 mph hurricane wind is ------ as strong as the force exerted on the same house by a 60mph gale wind

Four times Double the mass double the speed if wind speed doubles, the force goes up four times

A person starts from rest and begins to run. The runner puts a certain amount of momentum into her herself and ----- momentum into the ground.

The same amount momentum = force * time

Suppose an open railroad car is rolling without friction in a vertical-falling downpour and an appreciable amount of rain falls into the car and accumulates there. Consider the effect of the accumulating rain on the speed, momentum and kinetic energy of the car. The speed of the car will....

decrease Mass increases due to the accumulated rain and momentum is constant so the velocity decreases

Suppose there is a drain plug in the open railroad car rolling without friction with no more rain. The drain plug at the bottom of the rolling car allows the accumulated water to run out. The speed of the car will....

not change As the water is released from the car it exerts no force on the car so the speed of the car is not changed.

When all the molecules are bouncing about in different directions the clay as a whole does not move and it is called ----

thermal kinetic energy

A little sled weighs one pound. It is set in motion over frictionless ice by a toy rocket motor. After the rocket fuel is expended, the sled is coasting over the ice at one foot per second. How much force did the rocket exert on the sled to make it go?

unknown, not enough information F= m/a a - initial velocity- final velocity / time Do not know time

A one pound-lump of clay traveling at one foot per second smashes into another one -pound lump of clay which is not moving. They stick together and become a one two pound lump of clay. What proportion of the kinetic energy in the originally moving lump was turned into heat during the collision>

50% Since half of the speed is lost, their kinetic energies are 1/4 (.25+.25)

Suppose there is a drain plug in the open railroad car rolling without friction with no more rain. The drain plug at the bottom of the rolling car allows the accumulated water to run out. the momentum of the car will ... what about kinetic energy?

Decrease (both) The Departing water takes its momentum and kinetic energy with it

Consider a block of ice on a friction-free frozen lake. Suppose a continuous force acts on the block. Of course, this causes the block to accelerate. After the force has acted for some time the speed of the block has increased a certain amount. Suppose only the force is doubled while the mass and action time are unchanged, then the increase in speed will

Double force makes the speed change

Harry is finding it very difficult to muster enough torque to twist the stubborn bolt with a wrench and he wishes he had a length of pipe to place over the wrench handle to increase his leverage. He has no pipe, but he does have some rope. Will torque increase if he pulls just as hard on a length of rope toed to the wrench handle

NO The torque depends on applied force and length of the lever The rope increase the distance from the wrench, but not the lever arm The lever arm is the distance from the line of action

The Levi Strauss trademark shows two horses trying to pull apart a pair of pants. Suppose Levi had only one horse attached to the other side of the pant to a fencepost. Using only one horse would do what?

Not change the tension in the pants at all The post will pull back with the same force as the horse. No force on the pants

Momentum is inertia in motion and is equal to the product of a body's mass and its velocity. For example, if the speed of a projected cannonball is doubled, then the momentum is doubled. If instead the cannonball's mass is doubled then the momentum is doubled. Supposed, however, that a cannonball's mass is somehow doubled and its velocity also doubled. Then it's momentum....

Quadrupled momentum = mass * velocity impulse = change in momentum Ft = Delta mv

Mighty Mike weighs 200 lbs and is running down the football field at 8ft/s. Speedy Gonzales weighs only 100 lbs but runs 16 ft/s while Ponderous Poncho weighs 400 lbs and runs only 4 ft/s. Who will be more likely to break his bones?

Speedy Gonzales Because Speedy has more kinetic energy When you take double the speed, it takes double the time to stop, and four times the distance Penetrates four times as deep He is 1/4 of sixteen because he is one fourth the mass

A scientist is completely isolated inside a smoothly moving box that travels a straight-line path through space, and another scientists is completely isolated in another box that is spinning smoothly in space. Each scientist may have all the scientific goodies she likes in her box for the purpose for the detecting her motion in space. The scientist in which box....

Spinning box You know you are moving without consulting any background.

A rubber bullet and an aluminum bullet both have the same size, speed, and mass. They are fired at a block of wood. Which is most likely to damage the block

The aluminum bullet The momentum of the bullet is completely transferred to the block The bullet stops and surrenders all of its kinetic energy Puts more energy and less momentum (rubber is the reverse)

A rubber bullet and an aluminum bullet both have the same size, speed, and mass. They are fired at a block of wood. Which is most likely to know the block over.

The rubber bullet Both have equal momentum upon impact The rubber bullet bounces and has a greater impulse and the block provides a greater impulse to throw the bullet back out again The rubber bullet has up to twice the momentum upon the departure of the block

Mighty Mike weighs 200 lbs and is running down the football field at 8ft/s. Speedy Gonzales weighs only 100 lbs but runs 16 ft/s while Ponderous Poncho weighs 400 lbs and runs only 4 ft/s. In the encounter who will be more effective in stopping mike?

The same (8x200 = 100 x 16 = 400 x4)

Two identical cars of identical mass traveling at 55 mph, but in opposite directions crash head on into each other. Suppose one of the cars drives 55mph into an immovable stone wall. In which case does the car suffer more damage?

There is no difference. The immovable acts as a force mirror (Newton's Third Law) It puts out a force that is the reflection of the force applied

Consider a block of ice on a friction-free frozen lake. Suppose a continuous force acts on the block. Of course, this causes the block to accelerate. After the force has acted for some time the speed of the block has increased a certain amount. Suppose applied force mass and action are all as they were initially, but somehow the force of gravity doubled. (on another planet). Then the increase in speed will be....

Unchanged The increase in gravity increase the weight of the block, but not the mass or inertia. Inertia is what matters But if friction was involved, weight would matter because weight controls friction

Suppose an open railroad car is rolling without friction in a vertical-falling downpour and an appreciable amount of rain falls into the car and accumulates there. Consider the effect of the accumulating rain on the speed, momentum and kinetic energy of the car. The momentum of the car will be?

Unchanged The rain falls downward and has no horizontal momentum to add to the car

A cat runs across the floor form I to II to III without increasing or decreasing his speed. He only changes his direction of motion at II. Can we say for sure that a force was exerted on the cat at II?

Yes, there had to be a force on the cat at II If there was a no force the cat would continue straight The cat did not change speed because it was a sideways force which makes it turn A force pushing forward would increase the speed

Rotational motion is ---- and linear motion is -----

absolution relative

A person starts from rest and begins to run, the runner puts a certain amount of kinetic energy into herself and ----- kinetic energy into the ground

less energy = force * distance the distance of the earth and the runner are not the same, but the forces are. (runner moves farther, so all energy goes to runner)

A one-pound lump of clay traveling at on foot per second smashed into another one-pound lump of clay which is not moving. They stick together and become on two-pound lump, what is the speed of the two pound lump?

one half of one foot ft/s Any momentum lost by the moving lump goes into the one which was not moving. Multiply mass without changing momentum so speed decreases

When all the molecules are moving in the same direction, it is called -----

ordinary kinetic energy