Turn on thread page Beta
    • Thread Starter
    Offline

    8
    ReputationRep:
    Could someone give me a solution?

    A garden strimmer uses a piece of string rotating at 100rev s^-1 to trim grass. If the length is 15cm calculate the instantaneous velocity at the end of the chord.

    Thanks
    Offline

    21
    ReputationRep:
    (Original post by liverpool2044)
    Could someone give me a solution?

    A garden strimmer uses a piece of string rotating at 100rev s^-1 to trim grass. If the length is 15cm calculate the instantaneous velocity at the end of the chord.

    Thanks
    You know that the linear velocity is the distance covered in time, v=(2*pi*R)/T, where 2*pi*R is the circular distance (circumference), R is the radius of the orbit and T is the time period (time taken for one rotation). Since the angular velocity is w=theta/t (where theta is the angle travelled in radians and t is the time taken to travel that angle), or w=(2*pi)/T, the above equation becomes v=wR so you can simply substitute the numbers into the equation.

    Note that 1 revolution is 2pi radians.
    • Thread Starter
    Offline

    8
    ReputationRep:
    (Original post by Mehrdad jafari)
    You know that the linear velocity is the distance covered in time, v=(2*pi*R)/T, where 2*pi*R is the circular distance (circumference), R is the radius of the orbit and T is the time period (time taken for one rotation). Since the angular velocity is w=theta/t (where theta is the angle travelled in radians and t is the time taken to travel that angle), or w=(2*pi)/T, the above equation becomes v=wR so you can simply substitute the numbers into the equation.

    Note that 1 revolution is 2pi radians.
    Thanks alot mate, could you also help with this?

    A fairground round makes 9revs per minute. What is the angular speed?
    Offline

    21
    ReputationRep:
    (Original post by liverpool2044)
    Thanks alot mate, could you also help with this?

    A fairground round makes 9revs per minute. What is the angular speed?
    I gave you the angular velocity formula as w=theta/t (although you might have seen the equation as w=(2pi)/T, the other equation is a shortcut), so you just need to work out the angular distance, that is 9*2pi, and the time taken for it, that is 1minute*60)
    • Thread Starter
    Offline

    8
    ReputationRep:
    (Original post by Mehrdad jafari)
    I gave you the angular velocity formula as w=theta/t (although you might have seen the equation as w=(2pi)/T, the other equation is a shortcut), so you just need to work out the angular distance, that is 9*2pi, and the time taken for it, that is 1minute*60)
    I got 0.94 is that about right? Thanks in advance
    Offline

    22
    ReputationRep:
    (Original post by liverpool2044)
    I got 0.94 is that about right? Thanks in advance
    That is correct!
    Offline

    21
    ReputationRep:
    (Original post by liverpool2044)
    I got 0.94 is that about right? Thanks in advance
    I have not checked it but yeah, that should be correct
    • Thread Starter
    Offline

    8
    ReputationRep:
    Cheers
    Offline

    21
    ReputationRep:
    (Original post by liverpool2044)
    Cheers
    Don't forget the units
    Offline

    4
    ReputationRep:
    Isn't it
    100(2pi*r)/t = 100(2pi*0.15)/1

    because of the 100 revs per second. which then equals to 30pi = 94ms-1
    not 0.94?
    Offline

    21
    ReputationRep:
    (Original post by Siddhart1998)
    Isn't it
    100(2pi*r)/t = 100(2pi*0.15)/1

    because of the 100 revs per second. which then equals to 30pi = 94ms-1
    not 0.94?
    0.94 rad/s is the answer to the second question asked after the first question. Your answer is for the first one
    Offline

    4
    ReputationRep:
    (Original post by Mehrdad jafari)
    0.94 rad/s is the answer to the second question asked after the first question. Your answer is for the first one
    Ah okay.
    Safe G 👊
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: September 17, 2015

University open days

  1. University of Bradford
    University-wide Postgraduate
    Wed, 25 Jul '18
  2. University of Buckingham
    Psychology Taster Tutorial Undergraduate
    Wed, 25 Jul '18
  3. Bournemouth University
    Clearing Campus Visit Undergraduate
    Wed, 1 Aug '18
Poll
How are you feeling in the run-up to Results Day 2018?

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.