Physics - September 2007

When baseball outfielders throw the ball, they usually allow it to take one bounce on the theory that the ball arrives sooner this way. Suppose that after the bounce the ball rebounds at the same angle as it had when released but loses half its speed.

a. Assuming the ball is always thrown with the same initial speed, at what angle should the ball be thrown in order to go the same distance D with one bounce as one thrown upward at = 46.0° with no bounce?

b. Determine the ratio of the times for the one-bounce and no-bounce throws.
t1b / t0b =

2007-09-23 16:13:09 · 2 answers · asked by Anonymous

Just wondering what anyone thinks of it.

2007-09-23 16:02:26 · 2 answers · asked by Isaac C 1

I'm given a statement such as the vector position of a particle varies in time according to the expression r = (8.60 i - 8.40t^2 j) m.
Somehow, i have to find expressions for the velocity and acceleration as functions of time. (Using t, i, and j as necessary.); and determine the particle's position and velocity at t = 3.00 s.

Unfortunately, I'm not even sure how to rearrange it (or what its wanting me to rearrange into a function a T)

2007-09-23 15:40:09 · 1 answers · asked by phrozenwarrior 3

A particles position is given by the following expression:

r(t) = Rcos(wt)i + Rsin(wt)j

The magnitude of the velocity, |v(t)| (speed) is given by the expression:

sqrt((-Rwsin(t))^2 + (Rwcos(t))^2)

?Express the magnitude of the particle's acceleration in terms of R and v using the expression obtained for the speed of a particle?

____________________________

Please try to be concise and neat. Explain your steps if you can. Thanks in advance.

2007-09-23 15:13:46 · 1 answers · asked by Gills 1

Acceleration is generally defined as the time rate of change of velocity. When can it be defined as the time rate of change of speed?

2007-09-23 15:01:20 · 1 answers · asked by Anonymous

A common flea is recorded to have jumped as high as 21 cm. Assuming that the jump is entirely in the vertical direction and that air resistance is insignificant, calculate the time it takes the flea to reach a height of 7.0 cm. if this is the maximum height of the jump. Please show how you got the answer. I really need this tonight. Thanks!!!

2007-09-23 14:53:36 · 1 answers · asked by ☺♠JonasJay♫♦ 5

I've followed the answers of similar questions, but still seem to come up w/ the wrong answer, please help! :(

A basketball player 1.99m tall wants to make a basket from a distance 12.7m. The hoop is at a height of 3.05m.

If he shoots the ball (from a height of 1.99m) at a 61.7deg angle, at what inital speed must he throw the basketball so that it goes through the hoop w/o striking the backboard? .. answer in units m/s

2007-09-23 14:50:35 · 1 answers · asked by Anonymous

if you like, poked holes for head,feet and arms in a weather balloon, and get in, do you think i'll inflate?

2007-09-23 14:45:03 · 3 answers · asked by lucariojr 1

I was thinking, since you're further away from the Earth, is gravity less (even by a fraction of a percentage) in an aiplane?

2007-09-23 14:39:57 · 5 answers · asked by Jeff W 1

You pull with a force of 260 N on a rope that is attached to a block of mass 24 kg, and the block slides across the floor at a constant speed of 1.6 m/s. The rope makes an angle of 25 degrees with the horizontal.

2.)What is the y-component of the force exerted by the Earth on the block?

3.)What is the y-component of the force exerted by the floor on the block (sometimes called the "normal" force, because it is perpendicular to the floor)?

I can get the force of the rope on the block but cant get 2 and 3...any ideas?

2007-09-23 14:33:26 · 2 answers · asked by Anonymous

2007-09-23 14:29:08 · 14 answers · asked by Anonymous

2007-09-23 14:15:20 · 4 answers · asked by Anonymous

The velocity of a 150 gram ball changes from < 9, -7, 0 > m/s to < 9.2, -7.3, 0 > m/s in 0.04 s, due
to the gravitational attraction of the Earth and to air resistance.

I know net force and change in rate of mementum should be the same...but I don't know how to get either?

Thanks

2007-09-23 14:11:45 · 1 answers · asked by Anonymous

On a distant planet,the acceleration due to gravity is less than it is on earth.

2007-09-23 14:08:25 · 3 answers · asked by Anonymous

A spaceship ferrying workers to Moon Base I takes a straight-line path from the earth to the moon, a distance of 384,000 km. Suppose it accelerates at an acceleration 20.6 m/s^2 for the first time interval 15.7 min of the trip, then travels at constant speed until the last time interval 15.7 min, when it accelerates at -20.6 m/s^2, just coming to rest as it reaches the moon.

What is the maximum speed attained?
What total time is required for the trip?

I have tried so many ways to find the correct answer but i can't seem to do it right....please help

2007-09-23 14:05:28 · 2 answers · asked by sandymandy 1

2007-09-23 14:04:48 · 3 answers · asked by darechuk 3

a car is moving at a constant speed of 14m/s when the driver presses down the pedal for 11 seconds at an acceleration of 1.6m/s2. what is the average speed of the car???

2007-09-23 14:03:06 · 2 answers · asked by Daniela m 2

at which point it switches to slowing down with a constant acceleration of magnitude 0.12 m/s for 2.0 minutes. What was the average speed of the train during this time, that is, from starting at rest to the end of the 2.0 minutes of slowing down?


hint: think of it as two separate problems, one for the train speeding up, and one for the train slowing down; then put the two together to answer the question.

2007-09-23 14:00:07 · 1 answers · asked by myname_011 1

If a car moves with a constant speed, can you say that it also moves with a constant velocity? Please give an example of something because i don't understand this!!?!?

2007-09-23 13:57:25 · 3 answers · asked by Anonymous

a ball is thrown from the top of a building at an angloe of 58 to the horizontal and with an initial speed of 12.1m/s. The point of realease is 8.5m aobve the ground. find the horizontal range of the ball from the base of the building.

i have 17.41 as the answer but it's wrong....please give me a correct one.

2007-09-23 13:55:34 · 3 answers · asked by ljkim08 1

A lunar lander is making its descent to Moon Base I. The lander descends slowly under the retro-thrust of its descent engine. The engine is cut off when the lander is 5.0 m above the surface and has a downward speed of 0.8 m/s. With the engine off, the lander is in free fall.

What is the speed of the lander just before it touches the surface? The acceleration due to gravity on the moon is 1.6 m/s^2

i have no idea how to even approach the problem.....please help

2007-09-23 13:42:08 · 3 answers · asked by sandymandy 1

What is the instantaneous velocity of a freely falling object 10 s after it is released from a position of rest?
What is its average velocity during this interval?
How far will it fall during this time?

please provide an explanation to answers

2007-09-23 13:30:53 · 1 answers · asked by Igor S 1

neglecting air resistance.

2007-09-23 13:25:49 · 3 answers · asked by thugpreetforlife123 2

A 68.5 skater moving initially at 2.40 on rough horizontal ice comes to rest uniformly in 3.52 due to friction from the ice.

What is the friction force?

2007-09-23 13:20:28 · 1 answers · asked by Burt C 1

A cheetah can run at a maximum speed 110 km/h and a gazelle can run at a maximum speed of 80 km/h. If both animals are running at full speed, with the gazelle 91.6 m ahead, how long before the cheetah catches its prey? Answer in units of s.

2007-09-23 13:18:19 · 1 answers · asked by Anonymous

When you pay the electric company by the kilowatt-hour, what physical quantity are you actually paying for?

voltage
energy
current
power
none of the above

2007-09-23 13:17:51 · 4 answers · asked by WMC 1

2007-09-23 13:15:53 · 3 answers · asked by zoe 1

the one guy got the first part right this is the second part someone please help me its due tonite

2007-09-23 13:15:21 · 1 answers · asked by Shawn Carter 1

A passenger train is traveling at 29 m/s when the engineer sees a freight train 360m ahead traveling on the same track in the same direction. The freight train is moving at 6 m/s. If the reaction time of the engineer is .4s, what must be the deceleration of the passenger train if a collision is to be avoided?

If someone can help me with this I would greatly appreciate it!

2007-09-23 13:15:21 · 1 answers · asked by kathleen 1

there are no numbers for this problems....
to graph velocity versus displacement is very challenging...

2007-09-23 12:45:05 · 3 answers · asked by jack86 1