Homework Statement
Comment on the statement 'Today the temperature is 40\circC and yesterday it was 20\circC so it is twice as hot today as it was yesterday.'
The Attempt at a Solution
i feel that it is wrong to say that, although i think a body at 40\circC is twice as hot as a body at...
yeah you're right, i completely ignored that. a small current might not be able to operate the appliance.
errmm i still can't find the second reason... a hint would be great...lol
thnks
Homework Statement
Some electrical appliances are used with long cables to connect to them to the electrical supply. State and explain 2 reasons why these cables should have a low resistance per unit length.
The Attempt at a Solution
well for the long cables, a low resistance per...
Homework Statement
V = IR is used to define resistance. why can't it be used to define p.d.?
The Attempt at a Solution
i suggested that sometimes the current can be zero, but there is a p.d. so the equation does not hold.
but my teacher says that the answer is more towards the...
picture it this way, instead of doing the experiment in air, you are doing it in water.
what is the formula concerning the fringe separation? which of the parameters in it changes when the wave is traveling in water and not in air?
*edit* ooops alphysicist, i think we posted at the same time.
the force of friction is not 2664.5 N. It is (2664.5)(X) N, where 2664.5 N is the normal contact force and X is the coefficient of friction.
frictional force = normal contact force x coefficient of friction
it's more like a resultant force of 15N which moves the body 4/3 m when 20 J of work is done. the 15 N resultant force may include the force you apply - any resistive forces for example.
thnks borek and dynamicsolo. i understood the problem.
what if the plane is parallel to the equatorial plane, but it is above(or below) it, i.e. it does not pass through the centre?
the satellite will have to oppose the vertically downward force (when above the equatorial plane) in order to...
the centre of the orbit is at the centre of earth. the plane of the circular orbit if the satellite is above the equator is the same as the equatorial plane.
but if the satellite is not above the equator, the plane of the orbit will be at an angle with the equatorial plane. then there will...
Homework Statement
Explain why a geostationary satellite must be placed vertically above the equator.
Homework Equations
i know a GS has a period of 24 h,... and that it remains at a specific position with respect to a point on earth.
The Attempt at a Solution
i googled a bit...
* it's a matter of concepts.
in its 4th second of acceleration it passes 18m(ie during the 4th second, not after 4 seconds)
velocity at this instant is therefore 18 m/s
in its 5th second it passes 22m
velocity at this instant is 22 m/s
in 1 sec, there is a change of velocity from 18 m/s to...
that's what i initially thought. there has to be work done by the cyclist. but i needed an answer... :) at least i would get some marks somewhere.
there is no gain in Ek since there is no increase in speed. Maybe i should consider the direct conversion of chemical energy into heat and sound...
you have certain types of window glasses which do not allow passers by to see the passengers in the cars. it involves the principle of total internal reflection. people inside the car will be able to see outside while those outside will not be able to see inside the car. VIP cars have such...
Homework Statement
It is often stated that many forms of transport transform chemical energy into kinetic energy. Explain why a cyclist traveling at constant speed is not making this transformation. Explain what transformations of energy are taking place.
The Attempt at a Solution
1...
Homework Statement
An electric bulb is marked 120 V, 40 W.
(a) Calculate the current in this bulb when operating on a 120 V supply.
(b) Describe 3 different ways in which energy can be transferred from the filament when it is operating normally.
(c) If the light bulb is now connected to...
you are pulling the mass from the other side of the half cylinder right?
what is the resultant force acting on the mass at any point?
be careful when resolving the vectors.
also, it says the mass moves with constant velocity. resultant acceleration is zero.
what does this imply about...
the assumption we make is that whatever energy is taken from copper, it is totally transferred to the ice/water/water vapour.
for water:
you calculate the energy for:
1. increase in temperature of ice from -5 to 0 degrees.
2. melting of ice at 0 degrees.
3. increase in temperature of water...
for these types of questions, put the final temperature equal to x degrees. then consider the energy involved for both ice and copper to reach that temperature.
ice will increase from -5 to 0. then it will melt. it will then reach x degrees. hopefully x is not higher than 100 degrees, else you...
nooooooo... the acceleration-displacement graph is a negative gradient straight line, through origin. and the equation is a = -w^2X0
at least this is what we learn in high school...
then is it correct to say that the force against which friction acts is equal to the normal force of wall on ladder? it is when this normal force is greater than the frictional force that the ladder slides down... i got it right??
now what i can't understand is how we get the normal force of...
i don't understand how the weight of the man affects the frictional force as he moves up. the normal is equal to the weight of (ladder + man). both act in opposite directions, and as the man climbs up, the sum of weight remains the same.
though i do realize that this makes no sense. i can't...
i've not yet seen the attached file, it's not yet approved.
linear momentum = mv
now v = rw
w is angular velocity.
angular momentum = mrw
was that what you were asking?
the Ek lost is equal to the Ek initially minus the Ek final.
get an equation from this, and substitute the speeds in this equation by m and p.
e.g. 2p = m*u1
u1 = 2p/m
where u1 is the initial speed of mass m.
Homework Statement
A point mass rests on a horizontal platform which can be made to describe vertical s.h.m. of amplitude 0.10m and frequency 2.0 Hz. The mass makes contact with the platform as it rises from its lowest point. At what point, if any, will this contact be lost?
Homework...
it means that the 12V is supplying about 39W and the circuit is losing 31W of it as heat??
so only about 8W is useful??
am i right?? and smething else...is anyone having enough time to chck the other answers...coz i;m not so sure about them...
thank you and thnks astronuc
kirchhoff's second law...having exams soon, please help
Homework Statement
i got this circuit, in the attachment below. i was asked to find:
(1) I1 and I2
(2) the voltmeter reading (the voltmeter has one terminal connected at the point between the 2 ohm resistor and the 12V battery, say...
i still don't get it...
i found the normal to be -mg cos 'theta'
i took the angle to be between the weight vector and and the normal component to the circle.
i equated mg cos 'theta' to zero, but i can't seem to get anything.
i also tried equating centripetal force to the normal...
Thnks JoAuSc,...i understood the calculation part...started my calculations by equating force from stress to centripetal force instead...
what i still can't understand is what " the normal push of the rim on the ring just becomes zero when the wheel is rotating at angular speed 'omega' "...
Homework Statement
The strain in a rubber ring on a rim of a wheel of radius 0.40m is 3*10^-3 when the wheel is stationary. The normal push of the rim on the ring just becomes zero when the wheel is rotating at angular speed 'omega'. Calculate the value of 'omega' if Young's Modulus for the...
circular motion please
Homework Statement
a particle is slightly displaced from rest at the top of a fixed smoothsphere of radius r. Find the the vertical height through which the particle descends befor eleaving the sphere.
Homework Equations
f = (mv^2)/r
w = mg
The Attempt...
in this kind of problems, you should be breaking the motion into two. it is called resolving and 2 components are obtained. we most of the time use the vertical and horizontal component.
the initial velocity is the vector. it is at an angle 50(question 3). if you break this 60 ms-1 vector...
imagine a slope at an angle of say 30degrees(or theta) to the horizontal. you have a car on the slope moving downwards(not important). it has a weight perpendicular to the horizontal; and a contact force perpendicular to the slope, i.e. at 30degrees(or theta) to the horizontal. picture this...
correct me if I'm wrong, but i believe the equation v=u+at can be used, since this is a linear graph??
you know, u(initial velocity), and the product (at) is 0. the initial velocity is equal to the final velocity.
the best way to solve these kinds of problems is to find the appropriate equations and determine which of the quantity has to be common in the equations(usually two equations).
then equate these equations to find the unknown, which should be in one of the relevant equations.
another thing...my teacher told me that the centripetal force is a resultant force. considering question II, what is actually the force towards the centre of the loop, which gives a resultant force with weight, the centripetal force. i understaood what you meant 'learning physics' for this...
i have yet another question... when you are swirling smething attached to a string and doing circular motion. the weight is due to the mass of the body. But what causes the tension. the centripetal force is the resultant between the tension and weight. and what does the centrifugal force come to...
Two more questions:
III. A particle is moving in a circular path described by the equation:
'theta'= (3 rad s-2t^2) - (2 rad s-1)t
Calculate the angular velocity and the angular acceleration at t = 6.0s.
I'm tootally lost.
IV. A particle is slightly displaced from rest at the top of...
I. A hump back bridge has a radius of curvature of 40m. Calculate the max speed at which a car could travel across the bridge without leaving the road at the top of the hump.
I realized that weight - contact force at the top would give the resultant centripetal force.
But i have no...
i worked through [art of it, i don't know if its correct. You should first be caluculating the forces from the 3 charges on e2.
F1 = (k*e^2)/R^2
F3 = F4 = (k*e*-q)/(R/cos theta)^2
Now considering only the horizontal components, the vertical ones from F3 and F4 will cancel out.
F1 = 2 F3...