You pull a box w/ constant force across a frictionless table using an attached rope held horizontally. If you now pull a rope with the same force at an angle to the horizontal (with the box remaining flat on the table). does the acceleration of the box in
-it acceleration remains the same because it is pulled with constant force.
-accer. would decrease.
A bear sling is used in some national parks for placing backpackers food out of reach of bears. the the backpacker raises the pack by pulling down on the rope, the force needed:
the force increases b/c gravitational energy ?. in order to pull it up the rope must exert a vertical force equal to the backpacks weight.
A person stands on a scale in an elevator. his apparent weight will be the greatest when the elevator..?
accelerating upwards.
accerl ? the net force is ?
when a skier skis down a hill, the normal force exerted on the skier by the hill is.....?
equal to the weight of the skier.
A person on a scale in an elevator. His apparent weight will be the greatest when the elevator is..?
accelerating upwards
A 50N crate sits on a horizontal floor where the coefficient of static friction between the crate and the floor is .40. A 15N force is applied to the crate to the right. what is the resulting static friction force acting on the crate?
15N to the left
A car drives at steady speed around perfectly circular track. Which of the following is true?
both acceleration and net force on the car point inward.
Will the acceleration of a car be the same when a car travels around a sharp curve at a constant 60km/h as when it travels around a gentle curve at the same speed?
accer-how quick on changes velocity.
-when one goes around sharp turn the change in velocity is quicker than in a gently curve.
Is water removed from clothes in spin dryer by centrifugal force throwing the water outward?
no, water moves tangentially to the rotation, out the holes in a straight line; so water separates from clothes. no centripetal force throwing water outward, there is a lack of it to keep water moving in circular path.
A bucket of water can be whirled in a vertical circle without the water spilling out,even at the top of the circle when the bucket is upside down.Explain
on top of bucket grav. & normal forces are pointing downward, this provides centripetal force needed to keep water moving in a circle.
force acting perp. to its motion
Which of the following points towards the center of the circle in uniform circular motion?
acceleration and net force(net force is always in the same direction as acceleration).
A child whirls a ball in a vertical circle. Assuming the speed of the ball is constant, when would the tension in the cord connected to the ball be the greatest?
nowhere, the cord is stretched the same amount at all points.
Friction
resistance acting on an object as a result of the objects interaction w/ some material median.
Direction of force
-parallel to surface of contact.
- dynamic case:opposite direction of motion.
-static case:opposite direction of net applied force.
Relationship between normal force and friction
directly proportional. ? mass ? friction.
frictional force vs applied force
for an object starting at rest, the force of static friction increases linearly with the applied force up until the applied force reaches a value (usFn). At this point the object just begins to move, & the force of friction drops to a roughly constant val
When sliding a piece of furniture across the floor, why is it harder to get it to start moving than to keep in moving?
b/c it wants to stay at rest & has more friction once it starts moving friction ?
Why is force of friction independent of contact area?
more area=less interaction.
less area=more interaction.
(ie) stepping on one nail, stepping on 1000nails.
is it possible for an object moving with a constant speed to experience an acceleration?
yes, only if velocity is changing direction.
What is the direction on acceleration in a circle?
towards center.
how can an object move in curved path?
there must be a force on object that is perpendicular to its motion.
Centripetal Force
Any object that moves in a circular path experiences a centripetal that acts towards the center of the circle.
Centrifugal Force
gives rise to a reaction force that acts away the center of the circle called centrifugal force. this reaction force does not act on the object that moves in a circle
Force that provides object whirls in horizontal circle on end of string.
Tension of rope
Force that provides car going around curve
Friction
Force that provides person on rotor ride
Wall(normal force)
Force and mass relationship
direct
What happens to the force of attraction between objects if the mass of one object doubles?
force doubles
Force and distance relationship
inverse
What happens to the force of attraction between objects if the distance between the objects doubles?
force gets 4 times smaller
what would happen to your weight if you climbed to the top of mount everest?
distance between you & earth is bigger.
your weight would decrease since distance between you & the center of the earth would increase.
what keeps satellite up in its orbit around earth?
its speed (right speed-to low it would fall into earth to fast it will go off in straight line)
which pulls harder gravitational, earth on moon of moon on earth? which accelerates more?
force are the same, moon has greater acceleration.
while standing on scale in elevator, your apparent weight will be least when elevator..?
accelerates down or free fall.
at the surface of a certain planet, the gravitational acceleration g has a magnitude of 20m/s^2. A 10kg brass ball is transported to this planet. the mass of the brass ball on this planet is.
10kg
A hypothetical planet has a radius twice that of earth, but the same mass. what is its acceleration to gravity near its surface?
(?F=ma?[[[Gm1m2)/r^2)=ma]]])
A satellite in circular orbit around the Earth moves at constant speed. This orbit is maintained by the force of gravity between the earth & the satellite, yet no work is done on the satellite. how is this possible?
b/c direction on motion is perpendicular to the force.
if the speed of the particle doubles by a factor does its kinetic energy increase?
d?v^2
A 70 kg hiker starts at an elevation of 1200m & climbs to the top of a peak 2000m high. what is the hiker's change in potential energy?
560,000
a car traveling at a velocity v can stop in a minimum distance d. what would be the cars minimum stopping distance if it were traveling at a velocity of 2v?
d?v^2
A ball is thrown straight up. at what pt does the ball have the most energy? ignore air resistance.
everywhere; the energy of the ball is the same at all points
what happens to waters gradational P.E at top of waterfall to pool below.
at top of water has P.E then falls & transforms to K.E.
why is preferred to step over a log rather then to step down on it.
b/c it requires one to raise center of mass farther than just stepping over.
At hydroelectric power plant, water is directed at high speed against turbine blades should be designed so that the water..?
rebounds off the blades.
A super ball is dropped from a height h onto a hard steel plate from which it rebounds at nearly it original speed. If we consider the super ball to be our system durning this process then momentum is....?
not conserved for the process (inelastic energy?K.E is not conserved)
A 6500kg railroad car travels alone on a level frictionless track with a constant speed of 15m/s. A 2200kg load, initially at rest, is dropped onto a car. what will be the car's new speed?
11.2m/s
A baseball is pitched horizontally toward home plate with a velocity of 100km/h. In which of the following scenarios does the ball have the largest change in momentum.
the baseball is hit straight back to the pitcher at a speed of 100km/h.
A 15 kg hammer strikes a nail at a velocity of 8m/s and comes to rest in a time interval of 7ms. the average force acting on nail is..?
17kN
If the distance between two objects were to double, what would happen to the gravitational force between them..?
It would decrease by a factor of 4
Relationship between force and mass?
direct, is mass doubles ?force doubles
Relationship between force and distance?
inverse, if distance doubles?force gets 4 times smaller
K.E?W
a moving object can do work on another object it strikes by exerting a force on the object & making it move through a distance.
W?KE
doing work on object at rest gives it motion.
Conservative force
when work done by force on object in moving between 2 points is independent of the path taken. [[depends only on initial & final position]]
Nonconservative force
when work done by force on object in moving between 2 points depends upon the path taken.(ie, friction)
When one releases a ball from under chin, tied to a lever why doesn't it hit the person?
b/c he didn't put any work on it thus the P.E and gravity remained the same.
Conservation of energy principle
energy cannot be created nor destroyed;while energy can get converted from one form into another, the total energy of an isolated system remains constant.
when jumping from a fence to the ground why do you want to bend you knees?
goal is to min ?F. do this my Max time & Min momentum(((bending knees)))) makes one reduce speed thus min momentum.
Why does a karate expert prefer a quick blow to a long one?
goal is to max ?F. by min. time one exerts bigger force. and recoil of leg/arm help them maximize momentum.
Why do tennis players,golfers,home run hitters want to have a long follow through?
to max momentum. do this my max. time& force
If you were an auto safety engineer, how would you go about improving automobile safety?
make cars crunch up this will cause car collusion to increase time thus less force.
air bags->reduce force by increasing time.
this reduces pressure.
also cars have padded front.
what hurts most getting hit with a paintball that recoils or the breaks?
the paintball that breaks because bigger momentum (bigger impulses).
Elastic collusions
K.E is conserved.