Newton's second law of motion question
Hi I was wondering if anyone could help me with this question:
"Two particles of equal mass have been dropped from the same height (20m) above the earth's surface. The first surface is solid, and decelerates within 0.001s when it hits the ground. The second particle is malleable, so it decelerates at a much slower rate of 0.1s. Assuming that the only force acting on the particles is gravity, compute the force associated with each particle hitting the ground."
I know that F=ma and a=deltaV/deltaT
"Two particles of equal mass have been dropped from the same height (20m) above the earth's surface. The first surface is solid, and decelerates within 0.001s when it hits the ground. The second particle is malleable, so it decelerates at a much slower rate of 0.1s. Assuming that the only force acting on the particles is gravity, compute the force associated with each particle hitting the ground."
I know that F=ma and a=deltaV/deltaT
Original post by simon-123
Hi I was wondering if anyone could help me with this question:
"Two particles of equal mass have been dropped from the same height (20m) above the earth's surface. The first surface is solid, and decelerates within 0.001s when it hits the ground. The second particle is malleable, so it decelerates at a much slower rate of 0.1s. Assuming that the only force acting on the particles is gravity, compute the force associated with each particle hitting the ground."
I know that F=ma and a=deltaV/deltaT
"Two particles of equal mass have been dropped from the same height (20m) above the earth's surface. The first surface is solid, and decelerates within 0.001s when it hits the ground. The second particle is malleable, so it decelerates at a much slower rate of 0.1s. Assuming that the only force acting on the particles is gravity, compute the force associated with each particle hitting the ground."
I know that F=ma and a=deltaV/deltaT
use a suvat equation to figure out the velocity when the particles impact the surface.
Original post by raging_purple
use a suvat equation to figure out the velocity when the particles impact the surface.
v=u+at ?
Original post by simon-123
v=u+at ?
You don't have the amount of time it takes the particles to fall to the ground - only the distance they fell. Hence, I'd use v2=u2+2as. I hope that isn't giving too much away.
Original post by anosmianAcrimony
You don't have the amount of time it takes the particles to fall to the ground - only the distance they fell. Hence, I'd use v2=u2+2as. I hope that isn't giving too much away.
I don't think my lecturer has taught me this equation yet.
So v^2=0^2+(2*20000*20) ?
Original post by simon-123
I don't think my lecturer has taught me this equation yet.
So v^2=0^2+(2*20000*20) ?
So v^2=0^2+(2*20000*20) ?
Where are you getting the 20000 figure from?
Original post by raging_purple
Where are you getting the 20000 figure from?
20/0.001
Original post by simon-123
20/0.001
You need to work out the acceleration of the object when it's falling toward the surface.
The only force acting on it is gravity, so the force of gravity will be your acceleration.
Original post by raging_purple
You need to work out the acceleration of the object when it's falling toward the surface.
The only force acting on it is gravity, so the force of gravity will be your acceleration.
The only force acting on it is gravity, so the force of gravity will be your acceleration.
Oh right thanks!
Original post by simon-123
Hi I was wondering if anyone could help me with this question:
"Two particles of equal mass have been dropped from the same height (20m) above the earth's surface. The first surface is solid, and decelerates within 0.001s when it hits the ground. The second particle is malleable, so it decelerates at a much slower rate of 0.1s. Assuming that the only force acting on the particles is gravity, compute the force associated with each particle hitting the ground."
I know that F=ma and a=deltaV/deltaT
"Two particles of equal mass have been dropped from the same height (20m) above the earth's surface. The first surface is solid, and decelerates within 0.001s when it hits the ground. The second particle is malleable, so it decelerates at a much slower rate of 0.1s. Assuming that the only force acting on the particles is gravity, compute the force associated with each particle hitting the ground."
I know that F=ma and a=deltaV/deltaT
Both particles hit the ground at the same speed assuming no air resistance.
If you haven't seen the equation given by the other poster, then you can work out this speed by equating the object's potential energy at height 20m (mgh) to its kinetic energy on impact (½mv²)
They decelerate at different rates on impact.
Use v = u - at with u = the speed you calculated above for speed on impact.
v, final velocity, is zero when it finally comes to rest.
From the given value of t you can find a, the acceleration/deceleration in each case.
Then F=ma
There are other ways of doing this but it isn't clear what theory you've done so far.
You can also use F x time = change in momentum.
(edited 9 years ago)
Original post by raging_purple
You need to work out the acceleration of the object when it's falling toward the surface.
The only force acting on it is gravity, so the force of gravity will be your acceleration.
The only force acting on it is gravity, so the force of gravity will be your acceleration.
That's not what the question is asking for. It wants the force required to stop the object on impact.
(edited 9 years ago)
Original post by Stonebridge
That's not what the question is asking for. It wants the force required to stop the object on impact.
The velocity on impact is required to work out the deceleration.
I am only advising him on the first stage of the question as he already stated in his OP that he knows f=ma.
Original post by raging_purple
The velocity on impact is required to work out the deceleration.
I am only advising him on the first stage of the question as he already stated in his OP that he knows f=ma.
I am only advising him on the first stage of the question as he already stated in his OP that he knows f=ma.
Thanks. Got it!
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