Physics - October 2007

I have a couple of questions on relative motion
1. Two swimmers can swim equally fast relative to the water. they have a race to see who can swim across a river in the least time. Swimmer A swims perpendicular to the current and lands on the far shore downstream, because of the current. Swimmer B swims upstream at an angle to the current and lands on the shore directly opposite the starting point. Wo crosses the river in the least time. Explain your answer.

2. A ball is whirled on the end of a string in a horizontal circle of radius R and period T. If the period is increased by a facotr of 2 (keeping the radius constant), what speed must you have in the comparison to the original speed to maintain the same centripetal acceleration as before.

Any help will be much appreciated.

2007-10-11 12:09:10 · 2 answers · asked by Apoorva K 1

2007-10-11 11:45:46 · 1 answers · asked by Richard S 3

A certain frog's hind legs produce a force of 2.5 times its weight through a vertical distance of 9 cm, at which point the frog becomes airborne. A) What is the frog's speed at takeoff? B)What height about the ground does the frog reach?

the answers are 1.63 m/s and 13.5 cm

Please help me and show me how to do this
thanks!!

2007-10-11 11:44:46 · 1 answers · asked by J 2

A ball is thrown from the ground onto a roof of height 15 m from a distance of 7 meters away as shown in the diagram. The maximum height of the ball's trajectory is 3.4 meters above the top of the roof.


Find the initial horizontal component of the velocity.
??????
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(a) Find the required initial vertical component of the velocity, Vy.
Vy = m/s *
19 OK

HELP: The ball is at its maximum height. What does this tell us about Vf?




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(b) Find the time for the ball to reach maximum height.
t = s *
1.936 OK



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(c) Find the time for the ball to fall from the maximum height to the rooftop.
t = s *
.83 OK

2007-10-11 11:37:50 · 1 answers · asked by SEXXYSuzzy 1

A ball is thrown with an initial speed of 30 m/s at an angle of 45°.The ball is thrown from a height of 11 m and lands on the ground.

(a) Find the time of flight.
t = s


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(b) Find the maximum height.
h = m


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(c) Find the distance from where the ball is thrown to where it lands.
d = m


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(d) Find the speed at the impact.
v = m/s

2007-10-11 11:36:03 · 1 answers · asked by SEXXYSuzzy 1

A parachutist with a camera descends in free fall at a speed of 16 m/s. The parachutist releases the camera at an altitude of 70 m.
(a) How long does it take the camera to reach the ground?
b) What is the velocity of the camera just before it hits the ground?

i got 5.75 s and 44.2 m/s.... and got both wrong.... please help

2007-10-11 11:14:14 · 2 answers · asked by Pauly Walnuts 2

fired in a time of 10s Detemine the following
1)how fast was the bullet moving at half the maximum height

2007-10-11 11:09:32 · 1 answers · asked by Anonymous

Swimmer in River

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A river 700 ft wide flows with a speed of 10 ft/s with respect to the earth. A woman swims with a speed of 5 ft/s with respect to the water.
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a) If the woman heads directly across the river, how far downstream is she swept when she reaches the opposite bank?
d1 = ft *
1400 OK

HELP: Can you find the time it takes the swimmer to get across the river?
HELP: Can you use this time to find the distance down river she was pulled?


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b) If she wants to be swept a smaller distance downstream, she heads a bit upstream. Suppose she orients her body in the water at an angle of 37° upstream (where 0° means heading straight accross, as in part (a)), how far downstream is she swept before reaching the opposite bank?
d2 = ft


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c) For the conditions of part (b), how long does it take for her to reach the opposite bank?
t = s

2007-10-11 10:37:38 · 1 answers · asked by cuteeebabygirl 1

A 82 kg clock initially at rest on a horizontal floor requires 618 N horizontal force to set it in motion. After the clock is in motion, a horizontal foce of 561 N keeps it moving with a constant velocity.
The acceleration of gravity is 9.81 m/s^2.

A) Find μs between the clock and the floor.
B) Find μk between the clock and the floor.

Thanks for the help!!!!!

2007-10-11 10:33:02 · 1 answers · asked by jon s 2

Two vectors A and B each have magnatudes of 6.0 m and the angle between their directions is 60 degrees. Find AxB.
I know this is probably easy but I am still not sure.

2007-10-11 10:08:50 · 3 answers · asked by stang16041 1

The driver of an empty speeding truck slams on the brakes and skids to a stop in a distance Dm = 254.84 m. The truck's initial velocity is v0 = 50 m/s and its total mass is m = 3137.8 kg. The coefficient of kinetic friction between the tires and the road is uk = 0.5. If the truck were carrying an amount of cargo that doubled its total mass, what would its stopping distance have been? (Assume the road is straight and horizontal).

2007-10-11 10:02:22 · 3 answers · asked by Jerry M 1

A sky diver of mass 80.0 kg (including parachute) jumps off a plane and begins her descent.
Throughout this problem use 9.80 m/s^2 for the magnitude of the acceleration due to gravity.

A) At the beginning of her fall, does the sky diver have an acceleration? A: No; the sky diver falls at constant speed. B: Yes and her acceleration is directed upward. Or C: Yes and her acceleration is directed downward.

B) At some point during her free fall, the sky diver reaches her terminal speed. What is the magnitude of the drag force F-drag due to air resistance that acts on the sky diver when she has reached terminal speed?
Express your answer in newtons.

2007-10-11 09:50:15 · 2 answers · asked by Nick S 1

A gymnast of mass 70.0 kg hangs from a vertical rope attached to the ceiling. You can ignore the weight of the rope and assume that the rope does not stretch.

A) Calculate the tension T in the rope if the gymnast hangs motionless on the rope.
Express your answer in newtons.

B) Calculate the tension T in the rope if the gymnast climbs the rope at a constant rate.
Express your answer in newtons.

C) Calculate the tension T in the rope if the gymnast climbs up the rope with an upward acceleration of magnitude 1.30 m/s^2.
Express your answer in newtons.

D) Calculate the tension T in the rope if the gymnast slides down the rope with a downward acceleration of magnitude 1.30 m/s^2.
Express your answer in newtons.

2007-10-11 09:49:19 · 1 answers · asked by Nick S 1

Any help on this physics homework problem is appreciated. I've tried it and have no idea how to properly relate the energy equations to this scenario.

An engine-less space capsule is launched from the surface of the Earth and travels into space until it experiences essentially zero gravitational force from the Earth. The initial speed of the capsule is 18,500 m/s. What is its final speed? Assume no significant gravitational forces from other solar system bodies. Mass of Earth = 5.97e24 kg. Radius of Earth = 6.38e6 m.

2007-10-11 09:40:36 · 1 answers · asked by slay_09 2

basically i know that in snooker or billiards or pool when you hit the cue ball at a stationary object ball the paths they follow after collision are at right angles to each other. i was wondering if anybody knew any mathematical proof that shows that this is true.

2007-10-11 09:29:40 · 9 answers · asked by neil 2

A ball if thrown vertically upward with a speed of 1.53m/s from a point 4.21m above the ground. Calculate the time at which the ball will reach the ground. Include all the numbers and formulas you use to find the answer, even our teacher couldnt figure it out.

2007-10-11 09:05:15 · 5 answers · asked by Matt K 2

2007-10-11 09:02:29 · 4 answers · asked by Anonymous

Problem Set:Final Velocity and Displacement

1) A bike rider accelerates constatntly to a velocity of 7.5m/s during 4.5 sec. The bike's displacement is +19m. What was the initial velocity of the bike?


2)The pilot stops the same plane in 484m using a constant acceleration of 8.0m/s^2. How fast was the plane moving before braking began?


3)A person with a shoulder harness can survive a car crash if the acceleration is smaller than -300m/sec^2. Assuming constant acceleration, how far must the front end of the car collapse if it crashes at 101km/hr?


4) A car is initially sliding backwards down a hill at -25km/hr. ZThe driver changes the direction of the car. By the time the car's velocity is is + 35km/h, it is 3.2 m from its starting point. Assuming the car was uniformly accelerated, find the acceleration.



Please help me explain any answer, this will be very helpfull. Thank you:)

2007-10-11 08:57:49 · 3 answers · asked by Anonymous

A 20.0 wood ball hangs from a 2.10 -long wire. The maximum tension the wire can withstand without breaking is 600 . A 0.900 projectile traveling horizontally hits and embeds itself in the wood ball.

2007-10-11 08:48:50 · 2 answers · asked by gbutterfly339 1

A 20.0 wood ball hangs from a 2.10 -long wire. The maximum tension the wire can withstand without breaking is 600 . A 0.900 projectile traveling horizontally hits and embeds itself in the wood ball.

2007-10-11 08:44:10 · 1 answers · asked by gbutterfly339 1

t t = 0, an object is projected with a speed v0 = 35 m/s at an angle q0 = 20° above the horizontal.The axes on the diagram show the x and y directions that are to be considered positive.

For parts a-g, calculate the requested quantities at t = 7 s into the flight:
a) The vertical acceleration of the object:

ay = m/s2 *
-9.8 OK
b) Its horizontal acceleration:

ax = m/s2 *
0 OK
c) Its vertical velocity:

vy = m/s
d) Its horizontal velocity:

vx = m/s
e) The angle to the horizontal at which the object is traveling (an angle above the horizontal should be reported as a positive number; an angle below the horizontal should be reported as a negative number). Please give your answer in degrees.

angle = °
f) Its vertical displacement, from where it started:

y = m
g) Its horizontal displacement, from where it started:

x = m
h) At what time does the object reach its maximum height?

tymax = s

2007-10-11 08:35:27 · 1 answers · asked by Anonymous

A 1100 N crate is being pushed across a level floor at a constant speed by a force of 300 N at an angle of 20.0° below the horizontal.
(a)What is the coefficient of kinetic friction between the crate and the floor?

(b)If the 300 N force is instead pulling the block at an angle of 20.0° above the horizontal, what will be the acceleration of the crate? Assume that the coefficient of friction is the same as that found in (a).

I know the number is close to .2562 for (a). I was trying different things and that answer was within 10%, but I have no idea what I did, and no idea what I did wrong

2007-10-11 08:11:40 · 3 answers · asked by swimchic632 2

A sled weighing 61.0 N is pulled horizontally across snow so that the coefficient of kinetic friction between sled and snow is 0.100. A penguin weighing 73.0 N rides on the sled, as in Fig. P4.76. If the coefficient of static friction between penguin and sled is 0.700, find the maximum horizontal force that can be exerted on the sled before the penguin begins to slide off.

I'm a junior in an AP Physics class. I asked my intructor to explain this question, but he only confused me more....please help ASAP....it's due tonight....Best Answer points to first correct answers with a few explantions......thanks!

2007-10-11 07:49:17 · 4 answers · asked by Anonymous

2007-10-11 07:17:21 · 3 answers · asked by americababy 2

horizontal force of 19.2N. Find the speed of the block after it has moved 4.9m. answer in units of m/s.

2007-10-11 06:49:51 · 1 answers · asked by sexysaraxx 4

A thin rod has a length of 0.831 m and rotates in a circle on a frictionless tabletop. The axis is perpendicular to the length of the rod at one of its ends. The rod has an angular velocity of 0.894 rad/s and a moment of inertia of 1.14 x 10-3 kg·m2. A bug standing on the axis decides to crawl out to the other end of the rod. When the bug (whose mass is 5 x 10-3 kg) gets where it's going, what is the change in the angular velocity of the rod?

2007-10-11 06:34:23 · 1 answers · asked by txsweetpea512 1

2007-10-11 06:31:32 · 5 answers · asked by Anonymous

i need to know a method to find out hookes law constant..using a spring, metre ruler, masses and a retort stand..how would one do that??? :s please help

2007-10-11 06:08:22 · 3 answers · asked by rogla 3

2007-10-11 06:02:51 · 2 answers · asked by Anonymous

2007-10-11 05:39:35 · 2 answers · asked by Derek T 2