Psych Homework Test 2
If a ball is projected upward from the ground with 10 kg • m/s of momentum, what is Earth's momentum of recoil? Why do we not feel this?
Earths momentum of recoil is 10 kg(m/s), and we can not feel this because of how big earth is.
What is required to change the angular momentum of a system?
External torque
Calculate the force of gravity on the 1-kg mass if it were 1.3×107 m above Earth's surface (that is, if it were three Earth radii from Earth's center).
F = 1.1 N
An ostrich egg of mass m is tossed at a speed v into a sagging bed sheet and is brought to rest in a time t: Find the force acting on the egg when it hits the sheet.
F =m(v/t)
Find the change in the gravitational force between two planets if the masses of both planets are doubled but the distance between them stays the same.
Fnew/F = 4
Where do you weigh more: at the bottom of Death Valley or atop one of the peaks of the Sierra Nevada? Why?
You weigh more in Death Valley because you are closer to the center of Earth
What would the magnitude of the gravitational field be anywhere inside a hollow, spherical planet?
Zero N/kg
The center of gravity of a basketball is located _______.
at its geometrical center
Which exerts the greater impulse on a steel plate- machine gun bullets that bounce from the plate, or the same bullets squashing and sticking to the plate?
bullets that bounce
When traveling twice as fast your kinetic energy is increased _______.
by a factor of four
A boxer rides with the punch so as to reduce _______.
force
The torque exerted by a crowbar on an object increases with increased _______.
force and leverage distance
When you lift twice the load twice as high, in half the time, the increase in potential energy is _______.
four times
The work that is done when twice the load is lifted twice the distance is _______.
four times as much.
The tangential speed on the outer edge of a rotating carousel is _______.
greater than toward the center
Cassy can get more force on the bricks she breaks with a blow of her bare hand when _______.
her hand is made to bounce from the bricks
The constant G in Newton's equation _______.
makes the units of measurement consistent
A 4.4-kg fish swimming 1.5 m/s swallows an absentminded 1.0-kg fish swimming toward it at a speed that brings both fish to a halt immediately after lunch: Find the speed of the approaching smaller fish before lunch.
v=6.6 m/s
When two vehicles collide, momentum is conserved _______.
whether the collision is elastic or inelastic
A ball is thrown horizontally from a cliff at a speed of 10 m/s . You predict that its speed 1 s later will be slightly greater than 14 m/s . Your friend says it will be 10 m/s: Who is right?
you
Calculate the torque produced by a 60-N perpendicular force at the end of a 0.24-m-long wrench.
τ =14 Nm
If a trapeze artist rotates once each second while sailing through the air and contracts to reduce her rotational inertia to one-third of what it was, how many rotations per second will result?
ω = 3.00 rotations per second
Suppose a ball of putty moving horizontally with 1 kg·m/s of momentum collides with and sticks to an identical ball of putty moving vertically with 1 kg·m/s of momentum. What is the magnitude of their combined momentum?
1.41 kg·m/s
The force of Earth's gravity on a capsule in space will lessen as it moves farther away. If the capsule moves to twice its distance, the force toward Earth becomes
1/4
What will the kinetic energy of a pile driver ram be if it starts from rest and undergoes a 10 kJ decrease in potential energy?
10 KJ
Escape speed from Earth is any speed equal to or greater than __________.
11.2 km/s
Find the energy turned into heat
1100 J
How much work is done when you push a crate horizontally with 110 N across a 15-m factory floor?
1700 J
How much impulse stops a 46-kg carton sliding at 4.2 m/s when it meets a rough surface?
190
What impulse occurs when an average force of 11 N is exerted on a cart for 2.2 s ?
24
What is the momentum of an 8.6-kg bowling ball rolling at 3.0 m/s ?
26
If you push a crate horizontally with 100 N across a 10-m factory floor and the friction between the crate and the floor is a steady 70 N, how much kinetic energy does the crate gain?
300 J
A projectile falls beneath the straight-line path it would follow if there were no gravity. How many meters does it fall below this line if it has been traveling for 1 s? For 2 s?
5 m, 20 m
When the useful energy output of a simple machine is 100 J, and the total energy input is 200 J, the efficiency is _______.
50%
What is the magnitude of the gravitational force between two 1-kg bodies that are 1 m apart?
6.67 × 10 -11 N
If an input of 100 J in a pulley system increases the potential energy of a load by 60 J, what is the efficiency of the system?
60%
If the force of friction on the crate is a steady 70 N, find the KE gained by the crate.
600 J
If the mass of the egg is 0.70 kg , its initial speed is 2.0 m/s , and the time to stop is 0.20 s, find the average force on the egg.
7N
In terms of impulse and momentum, why do air bags in cars reduce the chances of injury in accidents?
Air bags decrease the force of impact and increase the time force is applied, so you get less force for a longer time.
Distinguish between linear momentum and angular momentum.
Angular momentum depends on the distribution of mass, whereas linear momentum depends on the total mass.
Why are all tides greatest at the time of a full Moon or new Moon?
At full Moon and new Moon, the tides from the Moon and the Sun add because they are in line with Earth.
Why is it easier to stop a lightly loaded truck than a heavier one that has equal speed?
Because the lightly loaded truck has less KE and will require less force to stop it
At what part of an elliptical orbit does an Earth satellite have the greatest speed? The lowest speed?
Greatest nearest Earth; lowest furthest from Earth
If a golf ball and a Ping-Pong ball both move with the same kinetic energy, can you say which has the greater speed? Explain in terms of the definition of KE. Similarly, in a gaseous mixture of heavy molecules and light molecules with the same average KE, can you say which have the greater speed?
If KEs are the same but the masses differ then the ball with the smaller mass will have greater speed
Suppose our experimenter repeats his experiment on a planet more massive than Earth, where the acceleration due to gravity is g=30 m/s2. When he releases the ball from chin height without giving it a push, how will the ball's behavior differ from its behavior on Earth? Ignore friction and air resistance. (Select all that apply.)
It will take less time to return to the point from which it was released.
If Earth shrank, but there was no change in its mass, then what would happen to your weight at the surface?
It would increase.
In which is momentum conserved: an elastic collision or an inelastic collision?
Momentum is conserved in elastic and inelastic collisions
How is a flywheel constructed to maximize its rotational inertia?
Most of the mass is concentrated far from the axis
For an Earth satellite in circular orbit, list all the values that do not change.
Only speed, gravitational force, and distance from Earth
For an Earth satellite in an elliptical orbit, list all the values that do change.
Speed, gravitational force, and distance from Earth
Two cars are raised to the same elevation on service-station lifts. If one car is twice as massive as the other, compare their gains of potential energy.
The car with twice the mass has twice the gain of potential energy.
Why doesn't the force of gravity change the speed of a satellite in circular orbit?
The force is at a right angle to the velocity.
Why is kinetic energy a constant for a satellite in a circular orbit but not for a satellite in an elliptical orbit?
The force of gravity is perpendicular to the motion in a circular orbit but not in an elliptical orbit
Fossil fuels, hydroelectric power, and wind power ultimately get their energy from _______.
The sun
Predict what will happen if you reduce the magnitude of the velocity of the green truck to a magnitude smaller than that of the red truck.
The trucks will stick together after the collision and move to the left.
Click "Reset." Now, predict what will happen if you increase the mass of the green truck so that it is greater than the mass of the red truck.
The trucks will stick together after the collision and move to the right
Click "Reset." Now, predict what will happen if you change the velocity of the red truck so that it has a magnitude smaller than that of the green truck but is negative.
The trucks will stick together after the collision and move to the right.
Click "Reset." Now, predict what will happen if you change the velocity of the red truck so that it has a magnitude smaller than that of the green truck but is positive.
The trucks will stick together after the collision and move to the right.
Before you click "Play," predict what will happen if the red and green truck with equal mass and equal magnitude of velocity collide.
The trucks will stick together after the collision and not move
If you are not wearing a seat belt in a car that rounds a curve, and you slide across your seat and slam against a car door, what kind of force is responsible for your slide: centripetal, centrifugal, or no force?
There is no force as viewed by someone outside the car. To them you move in a straight line.
When you whirl a can at the end of a string in a circular path, what is the direction of the force you exert on the can?
Toward the center of the circle
What happens to the strength of the gravitational field at the surface of a star that shrinks?
it increases
A slowly moving ship can have a greater momentum than a fast-moving racing car when _______.
its mass times velocity is greater than that of the car
The quantity that is called impulse can be measured by the _______.
product of force and time
When a big fish swims into an oncoming smaller fish and swallows it, the momentum of the two-fish system _______.
remains the same
When one does twice the work in twice the time, the power expended is _______.
the same.
Tidal forces in general are the result of
unequal forces acting on different parts of a body.
Emily holds a banana of mass m over the edge of a bridge of height h. She drops the banana and it falls to the river below: Use conservation of energy to find the speed of the banana just before hitting the water.
v =√2gh
