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Physics: Post your doubts here!

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

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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
 
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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)
 
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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 !
 
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