This is about MOMENTUM (Practice Test #3 Question #1)

In summary, a rock dropped from a high tower falls freely under the influence of gravity and will gain an equal amount of speed for each meter through which it falls. This means that the amount of speed gained will increase with each second, as the rock is accelerating. This is represented by the equation d=1/2gt^2, where d is the distance fallen at the end of t seconds.
  • #1
gcombina
157
3

Homework Statement


. A rock is dropped from a high tower and falls freely under the influence of gravity. Which one of the following statements concerning the rock as it falls is true? Neglect the effects of air resistance.(a) The rock will gain an equal amount of momentum during each second.

(b) The rock will gain an equal amount of kinetic energy during each second.

(c) The rock will gain an equal amount of speed for each meter through which it falls.

(d) The rock will gain an equal amount of momentum for each meter through which it falls.

(e) The amount of momentum the rock gains will be proportional to the amount of potential energy

that it loses.

Homework Equations


gravity which is equal to 9.8 m/s^2 => I am using 10 m/s^2 for simplicity

The Attempt at a Solution


(A) yes, its possible
(B) no, its not possible
(C) question:

If I have a rock and i throw it from the second floor (4 meters from the ground), wouldn't the rock gain the same speed as it goes down each meter? (lets assume is 10m/s^2 instead of 9.8 m/s ^2)

1 meter down and 1 second passes = 10 m/s
2 meter down and 2nd second passes = 20 m/s
3 meter down and 3rd second passes = 30 ms

so what I can see is that each second and each meter , the rock gains the same speed. So, it gains 10 m/s each meter and second down
 
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  • #2
For question c, I think you're wrong when you equate meters to seconds.

Remember that the distance fallen is s=1/2 g t^2 so in the first second its fallen 1/2g or 4.9m and in the second second its fallen is 2 g or 19.6m.
 
  • #3
(c) is asking about each meter the rock falls, not about each second.
Does the rock take the same amount of time to fall each meter?
 
  • #4
Simon Bridge said:
(c) is asking about each meter the rock falls, not about each second.
Does the rock take the same amount of time to fall each meter?
Yes? doesn't the rock take 1 second to reach to the next meter? a meter per second?? so it takes the same amount (that is the way i understand it) or DO THE SECONDS INCREASE?
 
  • #5
jedishrfu said:
For question c, I think you're wrong when you equate meters to seconds.

Remember that the distance fallen is s=1/2 g t^2 so in the first second its fallen 1/2g or 4.9m and in the second second its fallen is 2 g or 19.6m.
UH? sorry to difficult for me to understand. S = 1/2 g t^2? what is that?
 
  • #6
gcombina said:
Yes? doesn't the rock take 1 second to reach to the next meter? a meter per second??
If the rock takes 1s to reach the next meter all the time, then the speed must be constant.
But doesn't the speed of a falling object increase with time?
In which case, doesn;t that mean it falls further with each second?
 
  • #7
Simon Bridge said:
If the rock takes 1s to reach the next meter all the time, then the speed must be constant.
But doesn't the speed of a falling object increase with time?
In which case, doesn;t that mean it falls further with each second?
yes, it does increase with time as it is accelerating right? so the time doubles or what?
 
  • #8
so if the rocks is accelerating then no way can the speed be the same.

so C is wrong
 
  • #9
Can you tell me who a rock falls with a graph. I had this idea before

10 meter for the 1st second
20 meters for the 2nd second
30 meters for the 3rd second

something isn't right about this
 
  • #10
The equation you can get from the suvat equations.
##d=\frac{1}{2}gt^2##
... distance d fallen at the end of t seconds.
 
  • #11
thnks
 

Related to This is about MOMENTUM (Practice Test #3 Question #1)

1. What is momentum and how is it defined?

Momentum is a physical quantity that measures the motion of an object. It is defined as the product of an object's mass and velocity. In other words, momentum = mass x velocity.

2. How is momentum different from velocity?

Velocity describes the speed and direction of an object's motion, while momentum takes into account both the mass and velocity of an object.

3. What is the equation for calculating momentum?

The equation for calculating momentum is: momentum = mass x velocity. It is important to note that momentum is a vector quantity, meaning it has both magnitude and direction.

4. What is the unit of measurement for momentum?

The unit of measurement for momentum is kilogram meters per second (kg*m/s) in the SI (International System of Units) system. In other systems, it can also be measured in gram centimeters per second (g*cm/s).

5. How is momentum conserved in a closed system?

In a closed system, the total momentum of all objects before and after a collision or interaction remains constant. This is known as the law of conservation of momentum. In other words, the total momentum of a system does not change unless an external force acts on it.

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