Physics Work, Energy, Momentum and Power Homework
A 5-kg shark swimming at 1 m/s swallows an absent-minded 1-kg fish swimming toward it at 4 m/s. The speed of the shark after his meal is
1/6ms The shark weighted 5kg and it swallowed a fish a that weighted 1kg so that 6 (5 * 1) - (4 * 1) = 1 The Ans. is 1/6
A 5-kg fish swimming at 1 m/s swallows an absent-minded 1-kg fish at rest. The speed of the larger fish after lunch is
5/6m/s
A force of 50 N is applied to the end of a lever, which is moved a certain distance. If the other end of the lever moves one-third as far, how much force does it exert
50N * 3( frm the 1/3) = 150N
If a machine multiplies force by a factor of 4, what other quantity is diminished, and by how much?
Distance is diminished to one-quarter
Impulse involves the time that a force acts, whereas work involves the
Distance that a force acts.
Which has the greater momentum when moving a bullet or a container ship
Either depending on speed
A roller skate at rest may have
Energy
When the speed of a moving car is doubled, how much more Kinetic Energy does it have
Four Times as much Note: If Object Speed is Doubled Kinetic Energy is Quadrupled
Two identical golf carts move at different speeds. The faster cart has twice the speed and therefor has
Four times the kinetic energy
Distinguish between force and impulse
Impulse is force times a time interval
Follow through is important in golf because it results in a greater
Impulse on the ball
An impulse can be Increased by
Increasing the force or Increasing the Time interval.
A car is raised a certain distance in a service-station lift, thus giving it potential energy relative to the floor. If it were raised twice as high, how much more potential energy would it have
It would have twice as much potential energy
What does it mean to say that momentum is conserved
Momentum does not change.
The impulse-momentum relationship is a direct result of
Newton's 2nd law
Can you produce a net impulse on an automobile if you sit inside and push on the dashboard
No, Never
Both a 50-kg sack is lifted 2 meters from the ground and a 25-kg sack is lifted 4 meters in the same time. The power expended in raising the 50-kg sack is
P= f * d and g=10m/s^2 In this problem and both of the problems equal 1000J
The power required to exert 4-N force over 3 meters in 2 seconds is
Power Formula P=(f * d) / t (f=4N * 3m) /t 12J/2s = 6W The Ans P=6W
The power expended doing 100 J of work in 50 s is
Power problem (f) was / by (t) there was no distance. (f)= 100J /(t) 50s The Ans. P= 2W
A lunar vehicle is tested on Earth at a speed of 10 km/h. When it travels as fast on the Moon, is its momentum more, less, or the same
The Same
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 potential energy
An apple hanging from a limb has potential energy because of its height. If it falls, what becomes of this energy just before it hits the ground? When it hits the ground
The energy is Kinetic Energy Before it hits the ground; it is Thermal Energy After
Railroad car A rolls at a certain speed and makes a perfectly elastic collision with car B of the same mass. After the collision, car A is observed to be at rest. How does the speed of car B compare with the initial speed of car A
The speed of car B is equal to the initial speed of A
If the equally massive cars of the preceding question stick together after colliding inelastically, how does their speed after the collision compare with the initial speed of car A
Their speed is half the initial speed of car A
A 1000-kg car and a 2000-kg car are hoisted to the same height. Raising the more massive car requires
Twice as much work
In a simple machine, how much work is done when an input of 10 N acts over a distance of 5 m
W=f * d (f) = 10N * (d)=5m The Ans. W=50J
The work done in pushing a TV set a distance of 2 m with an average force of 20 N is
W=f * d (f) = 20N * (d) = 2m The Ans. W=40J
The second floor of a house is 6 m above the street level. How much work is required to lift a 260-kg refrigerator to the second-story level
W=f *d & g=10m/s^2 (f)=260kg * (d)=6m * (g) 10m/s^2 The Ans W=15600J
When two vehicles collide, momentum is conserved
Whether the collision is elastic or inelastic
A force sets an object in motion. When the force is multiplied by the time of its application, we call the quantity impulse, and an impulse changes the momentum of that object. What do we call the quantity force multiplied by distance
Work
Which requires more work: lifting a 50-kg sack a vertical distance of 2 m or lifting a 25-kg sack a vertical distance of 4 m
Work =f * d Both problems equaled 1000J
Calculate the work done when a 18N force pushes a cart 3.7
Work Formula W=f * d (f) = 18N * (d) 3.7m The Ans. W= 67J Note: (N.m) = J
Is it correct to say that, if No Net Impulse is Exerted on a system, then no change in the momentum of the system will occur
Yes, always
How much work is done on a satellite in a circular orbit about Earth
Zero
Recoil is noticeable if we throw a heavy ball while standing on roller skates. If instead we go through the motions of throwing the ball but hold onto it, our net recoil will be
Zero
Which has greater kinetic energy
a car of half the mass traveling at 60 km/hr
It is correct to say that impulse is equal to
a corresponding change in momentum
A cannon recoils while firing a cannonball. The speed of the cannon's recoil is relatively small because the
cannon has much more mass than the cannonball
To impart the Greatest Momentum to an object, you must
exert the Greatest Force over the Longest Time
When a cue ball strikes an 8 ball head-on in a game of pool, the cue ball
transfers its momentum to the 8 ball
