Physics Chapter 6 (in class/homework conceptual)
When you drop a pebble from height H, it reaches the ground with kinetic energy K if there is no air resistance. From what height should you drop it so it will reach the ground with twice as much kinetic energy?
2H
A car accelerates from rest to 30 km/hkm/h. Later, on a highway it accelerates from 30 km/hkm/h to 60 km/hkm/h.Which takes more energy, going from 0 to 30, or from 30 to 60?
30 to 60
When the speed of your car is doubled, by what factor does its kinetic energy increase?
4
When you drop a pebble from height H, it reaches the ground with speed V if there is no air resistance. From what height should you drop it so it will reach the ground with twice speed?
4H
What would be the car's minimum stopping distance if it were traveling at a velocity of 2v2v?
4d
Two balls are thrown off a building with the same speed, one straight up and one at a 45 degree angle.
Both hit the ground with the same speed.
You and your friend, who weighs the same as you, want to go to the top of the Eiffel Tower. Your friend takes the elevator straight up. You decide to walk up the spiral stairway, taking longer to do so. Compare the gravitational potential energy of you and your friend, after you both reach the top.
Both of you have the same amount of gravitational potential energy at the top.
Two frisky otters slide down frictionless hillsides of the same height but different slopes. The slope of the hill of otter 1 is 30°, while the slope of the hill of otter 2 is 60°. If both start from rest, which otter is moving faster when she reaches the bottom of her hill?
Both otters have the same speed at the bottom.
A ball is thrown straight up.At what point does the ball have the most energy? Ignore air resistance.
Everywhere; the energy of the ball is the same at all of these points.
Suppose our experimenter repeats his experiment on a planet more massive than Earth, where the acceleration due to gravity is g=30 m/s2g=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?
It will take less time to return to the point from which it was released.
Why does the car's mass not matter?
Since both the change in kinetic energy and the work done by friction are proportional to the mass. The mass cancels out of the equation. Submit
A heavy frog and a light frog jump straight up into the air. They push off in such away that they both have the same kinetic energy just as they leave the ground. Air resistance is negligible. Which of the following statements about these frogs are correct? (There could be more than one correct choice.)
The lighter frog goes higher than the heavier frog. Just as they leave the ground, the lighter frog is moving faster than the heavier frog.
A ball is thrown straight up.Neglecting air resistance, which statement is not true regarding the energy of the ball?
The potential energy decreases while the ball is going up.
What is horsepower?
The rate at which the engine can do work.
A person stands on the edge of a cliff. She throws three identical rocks with the same speed. Rock X is thrown vertically upward, rock Y is thrown horizontally, and rock Z is thrown vertically downward. If the ground at the base of the cliff is level, which rock hits the ground with the greatest speed if there is no air resistance?
They all hit the ground with the same speed.
A heavy rock and a light rock are dropped from the same height and experience no significant air resistance as they fall. Which of the following statements about these rocks are correct? (There could be more than one correct choice.)
When they reach the ground, the heavier rock has more kinetic energy than the lighter rock. Both rocks have the same speed when they reach the ground.
The planet Earth travels in a circular orbit at constant speed around the Sun. What is the net work done on the Earth by the gravitational attraction between it and the Sun in one complete orbit? Assume that the mass of the Earth is given by MeMeM_e, the mass of the Sun is given by MsMsM_s, and the Earth-Sun distance is given by resresr_es.
Work is Zero
You have just moved into a new apartment and are trying to arrange your bedroom. You would like to move your dresser of weight 3,500 NN across the carpet to a spot 5 mm away on the opposite wall. Hoping to just slide your dresser easily across the floor, you do not empty your clothes out of the drawers before trying to move it. You push with all your might but cannot move the dresser before becoming completely exhausted. How much work do you do on the dresser?
Work is Zero
constant speed, net work is
ZERO
the net work done on an object is equal to the
change in kinetic energy of object
total mechanical energy is conserved if there's only
conservative forces
if mass doubles, kinetic energy
doubles
Joe and Bill throw identical balls vertically upward. Joe throws his ball with an initial speed twice as high as Bill. If there is no air resistance, the maximum height of Joe's ball will be
four times that of Bill's ball.
the work done in lifting an object has been stored as
gravitational potential energy
if kinetic energy goes from little to zero then
it was converted to potential
driving up speedy incline, work done by gravitational force is
negative
you carry object horizontally at a constant velocity
no work
you exert force but the object has no displacement
no work
is it possible for any hill to be taller than the first hill for a roller coaster?
no, the cart won't make it up
You push very hard on a heavy desk, trying to move it. You do work on the desk:
only if it starts moving.
nonconservative depend on
path taken
car moves in negative x direction so kinetic energy is
positive
as rock falls from rest with only potential energy
pot energy decreases but kinetic increases
as you go down hill
potential energy decreases
as you go up hill
potential energy increases
if mass doubles, speed
quadruples
work is
scalar, only positive or negative
When you throw a pebble straight up with initial speed V, it reaches a maximum height H with no air resistance. At what speed should you throw it up vertically so it will go twice as high?
square root of 2 * V
conservative forces only rely on
starting and ending positions
if net work is zero during certain time period
the initial and final kinetic energy were the same
if the force is in the opposite direction of velocity
the work done is negative
what's work of an object undergoing circular motion
work is zero