Wednesday
March 29, 2017

Post a New Question

Posted by on .

A merry-go-round (pictured) is sitting in a playground. It is free to rotate, but is currently stationary. You can model it as a uniform disk of mass 190 kg and radius 100 cm (consider the metal poles to have a negligible mass compared to the merry-go-round). The poles near the edge are 90 cm from the center.

Someone hits one of the poles with a 8 kg sledgehammer moving at 18 m/s in a direction tangent to the edge of the merry-go-round. The hammer is not moving after it hits the merry-go-round.

How much energy (modulus of (deltaE)) is lost in this collision? (enter a positive number for the absolute value in Joules)

  • PHYSICS - ,

    example of inelastic collision, where momentum before = momentum after, and simply calculate the difference in energy then!

  • PHYSICS - ,

    hi enjoy, what is the use of radius here?

  • PHYSICS - ,

    1/2 *[(m_1*m_2)/m_1+m_2)]*v_1^2

  • PHYSICS - ,

    So Anonymous you got 964.29 N??

  • PHYSICS - ,

    First, get all the variables:

    m_1: The mass of the merry-go-round
    m_2: The mass of the sledgehammer
    v_1: The velocity of the merry-go-round before the collision
    v_2: The velocity of the sledgehammer before the collision
    v_1': The velocity of the merry-go-round after the collision
    v_2': The velocity of the sledgehammer after the collision

    Apply the conservation of momentum:

    (m_1*v_1)+(m_2*v_2)=(m_1*v_1')+(m_2*v_2')

    You know everything except for v_1', so you can solve the above equation for v_1'. Then look at the difference in kinetic energy before and after the collision:

    ((0.5*m_1*v_1^2)+(0.5*m_2*v_2^2))-((0.5*m_1*v_1'^2)+(0.5*m_2*v_2'^2))

    The above is your answer.

  • PHYSICS - ,

    Honor Code: This exam is intended to test your personal understanding of the material. You may use everything on the 8.01 edX site as well as any textbooks you find useful. However, any discussion with other students or searching online for solutions to these questions is a violation of the honor code. The forum will remain open for you to read existing posts but new posts will be disabled until the exam closes. We will set up a wiki page for you to inform us of any site problems. Please confine your wiki entries to technical problems only, the staff cannot answer any physics questions. Use of the wiki to post hints or answers to exam problems is a violation of the honor code.

  • PHYSICS - ,

    so the radius is not important???
    and we'll have to consider v_1=0 and v_2'=0

  • PHYSICS - ,

    First Calculate the KE of the sledge hammer.
    2: Calculate the speed of the Merry-go-round (MGR) from m1.v1+m2.v2=m1.v1'+m2.v2'. Note: v2 and v1' are zero
    3: Calculate angular KE of the MGR
    4: Lost energy =1-3

    So if you can't solve this then you should go to elementary school

Answer This Question

First Name:
School Subject:
Answer:

Related Questions

More Related Questions

Post a New Question