physics

[ruby92]

A measurement of 327.66ms-1 accurate to 3%
which of the following gives her result expressed to the appropriate no of significant figures?
a) 327.7 b)328 c)330 d)300

[ruby92]

the current in a resistor is marked as (2.50+/-0.05)mA
the resistor is marked as 4.7 +/- 2% ohms
if these values were used to calculate the power dissipated what is the percentage uncertanity
a) 2% b) 4% c)6% d) 8%

[A.T]

the current in a resistor is marked as (2.50+/-0.05)mA
the resistor is marked as 4.7 +/- 2% ohms
if these values were used to calculate the power dissipated what is the percentage uncertanity
a) 2% b) 4% c)6% d) 8%

For resistance the percentage uncertainity is given which is 2%
For current u can find it by 0.05/2.5 * 100 = 2%
The formula is P=I^2 * R
so we'll multiply the current's uncertainity by 2 which will give 4%
now add both % uncertainities = 4+2=6%
hence answer is C

[ruby92]

but current is given a mA we dont take the 'm' into account here?
and dont u have to find the fractional uncertanity for both and add them?

[A.T]

but current is given a mA we dont take the 'm' into account here?
and dont u have to find the fractional uncertanity for both and add them?

For uncertainity u dont have to count the milli but for findind the actual power u will need to count it.
The simplest way to find the % uncertainity is find the % unc. of all the variables and add then so there is no neeed to find fractional unc.

[ruby92]

thnkx this actually makes sense 

[ruby92]

the ans to the first question is c 330ms-1...
any ideas

[astarmathsandphysics]

Because 330 is in the range 327.66 -3% to 327.66+3%

[ruby92]

thnkx

[ruby92]

A balloon is ascending with a uniform vertical velocity of 10ms-1.when at a height of 600m above the ground. A stone is dropped from it.
how long does the stone take to strike the ground?
with what velocity does the stone strike the ground

ASAP please
thnkx

[A.T]

Because 330 is in the range 327.66 -3% to 327.66+3%

Arent all the values in that range?
i dont think this is the correct logic.

[ruby92]

an arrow is shot horizontally at a target 20m away.The arrow hits a point 19.6cm verically below the point it was aimed at.Calculate the speed with which the arrow left the bow.


could someone please explain this and the above questions...urgently!!!!

[astarmathsandphysics]

y=1/2at^2
0.196=4.9t^2 so t=0.2 seconmd
v=x/t=20/0.2 =100m/s

[ruby92]

hw did u get 4.9 as the acceleration

[A.T]

hw did u get 4.9 as the acceleration

9.81/2
9.81 = g