Momentum & Energy Homework: Calculating Velocity After Book Throws

  • Thread starter Thread starter clarkandlarry
  • Start date Start date
  • Tags Tags
    Energy
AI Thread Summary
The discussion revolves around a physics homework problem involving a student on a frictionless surface who throws two books in opposite directions. The key focus is on applying the law of conservation of momentum to determine the student's velocity after throwing the biology book. Participants emphasize the importance of calculating the combined momentum of the system before and after the throws, noting that the total momentum remains zero. There is uncertainty about which equations to use and how to calculate the individual momenta of the student and the books. Understanding these principles is crucial for solving the problem effectively.
clarkandlarry
Messages
20
Reaction score
1

Homework Statement


A 64kg student is standing in the middle of a frozen pond with a frictionless surface while carrying 2 books, a physics book with a mass of 2.5kg and a biology textbook with a mass of 3.5kg. The physics book is thrown with a speed of 6m/s relative to the student to the right and then the biology book is thrown in the opposite direction with a speed of 4m/s relative to the student. Calculate the velocity of the student after the biology book is thrown.


Homework Equations


Not entirely sure
E = 1/2mv(squared)??


The Attempt at a Solution



I don't have a clue how to start this question. Please any help would be greatly appreciated.
 
Physics news on Phys.org
There are 3 objects under consideration: The student, the physics book, and the biology book.

Start by considering the law of conservation of momentum. What is the combined momentum of all three before and after the collision? What is the momentum of each individual object before and after the collision? How are these related?
 
Would the combined momentum be 0 before and after the collision?
 
Yes.
 
but how would i calculate the velocity of the person after he throws each textbook? i don't understand what equation (s) i would use.
 
Thread 'Variable mass system : water sprayed into a moving container'
Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
I was thinking using 2 purple mattress samples, and taping them together, I do want other ideas though, the main guidelines are; Must have a volume LESS than 1600 cubic centimeters, and CAN'T exceed 25 cm in ANY direction. Must be LESS than 1 kg. NO parachutes. NO glue or Tape can touch the egg. MUST be able to take egg out in less than 1 minute. Grade A large eggs will be used.
Back
Top