Physics: Post your doubts here!

[smzimran]

When jumping from a wall onto the ground, it is advisable to bend one's knees on landing. Using Newton's second law of motion, explain why it is sensible to bend one's knees..?

smzimran Could you help me here?

If you jump off a table, as your feet hit the floor, you let your legs bend at the knees in order to mimimize the force applied to your skeletal system.
Just before you reach the floor your body has momentum.
After you land, your body will have no momentum, so therefore there was a change in momentum and an impulse was necessary for this to happen.

The impulse on your body in this case comes from the floor and the size of the impulse is constant. Since impulse is the product of the force and the time over which it acts, then force and time are inversely proportional. So, if the force acts over a longer time period, then it will have a smaller magnitude. If we didn't bend our knees, the force would act over a much shorter period of time and would thus be much greater in magnitude, great enough to break our bones.

 

[nightrider1993]

a)(70-0)/0.0005 = 140,000

F=ma
= 0.046 x 140,000
= 6440 N


b) F=ma
6440= mx 9.81
m = 656.47 kg

answer provided by badrobot14

lol, that simple,eh...

 

[elbeyon]

Can anyone help me out for this question:
The answer is B.

 

[nightrider1993]

Can anyone help me out for this question:
The answer is B.

Remember that the voltage in parallel is same.

For top part:
The voltage across 500 resistor (PX) is 4 volts:
Voltage across PX= (500/1500)*12 = 4 V

For bottom part:
The voltage across 2000 resistor (PY) is 8 volts:
Voltage across PY= (2000/3000)*12 = 8V

Therefore, voltage across XY= 8-4 = 4 V

 

[nightrider1993]

When jumping from a wall onto the ground, it is advisable to bend one's knees on landing. Using Newton's second law of motion, explain why it is sensible to bend one's knees..?

smzimran Could you help me here?

The Force break up into different components, ie, horizontal and vertical components. Therefore less force is applied on the tibia and femur (skeletal bones)

 

[elbeyon]

Remember that the voltage in parallel is same.

For top part:
The voltage across 500 resistor (PX) is 4 volts:
Voltage across PX= (500/1500)*12 = 4 V

For bottom part:
The voltage across 2000 resistor (PY) is 8 volts:
Voltage across PY= (2000/3000)*12 = 8V

Therefore, voltage across XY= 8-4 = 4 V

Thanks a lot dude !

 

[nightrider1993]

Thanks a lot dude !

No problem. Glad i could help

 

[InnocentAngel]

All what u have to do is 0.3/t=0.01
Find t=30 s
so give and estimate of number of oscillations in 30 s....
simple

Hey friend i can't still understand it . Could you elaborate please please please
Thank you.

 

[nightrider1993]

Hey friend i can't still understand it . Could you elaborate please please please
Thank you.

Wa dont u get???

 

[Beca1206]

Can anyone pls upload may/june 2012 paper 2 with the answer sheet pls?

 

[Minato112]

Can anyone pls upload may/june 2012 paper 2 with the answer sheet pls?

Variance 1
Paper : http://olevel.sourceforge.net/papers/9702/9702_s12_qp_21.pdf
Marking Scheme : http://olevel.sourceforge.net/papers/9702/9702_s12_ms_21.pdf

Variance 2
Paper : http://olevel.sourceforge.net/papers/9702/9702_s12_qp_22.pdf
Marking Scheme : http://olevel.sourceforge.net/papers/9702/9702_s12_ms_22.pdf

 

[raamish]

do coherent waves only produce constructive intereference ?

 

[leosco1995]

do coherent waves only produce constructive intereference ?

AFAIK, they can also produce destructive interference.

Can someone help me with Q1 (c) of this paper? I don't get it.

 

[bamteck]

Someone please help me for june 2007 p2 no. 1

 

[Bilal Khan]

Someone please help me for june 2007 p2 no. 1

what help do u need??

 

[bamteck]

what help do u need??

for the no. 1
I can't understand what to do

 

[Albert Einstein]

what help do u need??

Use a compass set mark out angles 40 degrees for 20 then 40 for the appropriate angle from the graph n cntinues until 80

 

[bamteck]

Use a compass set mark out angles 40 degrees for 20 then 40 for the appropriate angle from the graph n cntinues until 80

A bit confusing for me

 

[Albert Einstein]

A bit confusing for me

Confused abt ??.. u knw hw to use a protactor...so refer to the graph at 20 x 10^-3 the angle is 40 degree so using the protactor find the postion for 20 x 10^-3 in the meter ??

 

[bamteck]

Confused abt ??.. u knw hw to use a protactor...so refer to the graph at 20 x 10^-3 the angle is 40 degree so using the protactor find the postion for 20 x 10^-3 in the meter ??

And for the (a)(ii) ?