Kinematics, Conservation of energy, momentum

In summary, the problem involves a mass of 8 kg exploding into two pieces and you need to use the conservation of momentum equation, m1 + m2 = 8, to solve for the mass of the small piece that hits the ground first. You also need to assume zero initial velocity for the pieces.
  • #1
wcjy
73
10
Homework Statement
An object of mass 8 kg explodes into two pieces at a height of 30 m from
the ground. Both small pieces fly out vertically. After 2 seconds of explosion, one
piece arrives the ground while the other piece is 16 m above the ground. Find the
mass of the small piece that hit the ground first.

Honestly i have no idea what type of question is this and how to approach this.
Relevant Equations
Kinetic energy = 0.5mv^2
Potential energy = mgh
m1 + m2 = 8
COE
0.5(m1)(u1)^2 + (m1)(g)(30) + 0.5(m2)(u2)^2 + (m2)(g)(30) = 0.5(m1)(v1)^2 + 0.5(m2)(v2)^2 + (m2)(g)(16)

Can you check if my eqn is correct? And can you advise what to do after this?
I wanted to do COLM but i don't know what is the initial part.
 
Physics news on Phys.org
  • #2
wcjy said:
Homework Statement:: An object of mass 8 kg explodes into two pieces at a height of 30 m from
the ground. Both small pieces fly out vertically. After 2 seconds of explosion, one
piece arrives the ground while the other piece is 16 m above the ground. Find the
mass of the small piece that hit the ground first.

Honestly i have no idea what type of question is this and how to approach this.
Relevant Equations:: Kinetic energy = 0.5mv^2
Potential energy = mgh

m1 + m2 = 8
COE
0.5(m1)(u1)^2 + (m1)(g)(30) + 0.5(m2)(u2)^2 + (m2)(g)(30) = 0.5(m1)(v1)^2 + 0.5(m2)(v2)^2 + (m2)(g)(16)

Can you check if my eqn is correct? And can you advise what to do after this?
I wanted to do COLM but i don't know what is the initial part.
That equation could be useful if you wanted to find the speed with which the small piece hit the ground, but you don't care about that.
What other conservation law might apply?
 
  • Like
Likes Delta2
  • #3
haruspex said:
That equation could be useful if you wanted to find the speed with which the small piece hit the ground, but you don't care about that.
What other conservation law might apply?
Conservation of momentum?
 
  • #4
wcjy said:
Conservation of momentum?
Right. Across what event?
 
  • #5
haruspex said:
Right. Across what event?
the explosion of the 8kg mass?
 
  • #6
wcjy said:
the explosion of the 8kg mass?
Yes.
 
  • #7
haruspex said:
Yes.
but i thought it does not have initial velocity so i can't apply it in the formula
 
  • #8
wcjy said:
but i thought it does not have initial velocity so i can't apply it in the formula
The question as stated in post #1 does not make it clear, but you will have to assume zero initial velocity. Why is that a difficulty?
 
  • #9
haruspex said:
The question as stated in post #1 does not make it clear, but you will have to assume zero initial velocity. Why is that a difficulty?
does that mean the eqn for colm is:
8*0 = m1(v1) + m2(v2)
 
  • #10
wcjy said:
does that mean the eqn for colm is:
8*0 = m1(v1) + m2(v2)
Yes.
 

FAQ: Kinematics, Conservation of energy, momentum

What is kinematics?

Kinematics is the branch of physics that studies the motion of objects without considering the forces that cause the motion. It involves concepts such as displacement, velocity, acceleration, and time.

What is conservation of energy?

Conservation of energy is a fundamental principle in physics that states that energy cannot be created or destroyed, only transformed from one form to another. This means that the total energy in a closed system remains constant.

What is momentum?

Momentum is a measure of an object's motion, and it is defined as the product of its mass and velocity. In other words, it is the quantity of motion an object possesses. The unit of momentum is kg*m/s.

How is energy conserved in a system?

In a closed system, energy can change from one form to another, but the total amount of energy remains constant. This is known as the law of conservation of energy. In other words, the total energy at the beginning of a process must equal the total energy at the end of the process.

How does momentum relate to Newton's laws of motion?

According to Newton's laws of motion, the momentum of an object will remain constant unless acted upon by an external force. This is known as the law of conservation of momentum. It means that in a closed system, the total momentum before an event must equal the total momentum after the event.

Similar threads

Inelastic collisions -- how is momentum conserved but not energy?
Replies
5
Views
2K
Elastic collision between two balls with different masses
Replies
8
Views
4K
Elastic head-on collision problem
Replies
8
Views
2K
Conservation of momentum & energy
Replies
11
Views
1K
Conservation of momentum - with understanding
Replies
2
Views
2K
Two dimensional momentum problem
Replies
20
Views
2K
Kleppner - blocks and a compressed spring
Replies
3
Views
3K
Energy conservation for objects hanging from a pulley
Replies
6
Views
2K
Momentum in a perfectly inelastic collision
Replies
6
Views
1K
Two manned satellites approaching one another
Replies
4
Views
4K

Hot Threads

Recent Insights

Back
Top