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Math Help - Dynamics Question

  1. #1
    Member looi76's Avatar
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    Dynamics Question

    Question:
    A car pulls a trailer with a force of 150N. This is shown in the diagram.

    (a) According to Newton's third law, forces exist in pairs.
    (i) What is the other force that makes up the pair?
    (ii) Write down the size and direction of this force?

    (b) The mass of the trailer is 190kg. As it sets off from rest, there is a resistive force of 20N.
    (i) Calculate the size and direction of the resultant force on the trailer.
    (ii) Calculate the initial acceleration of the trailer.

    (c) The force from the car on the trailer is maintained at 150N.
    When the car and trailer are traveling at constant speed.
    (i) What is the size of the resultant force on the trailer.
    (ii) Write down the size and direction of the resultant force on the trailer.

    Don't know how to start!...
    (a) The car and the trailer are the pairs?
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  2. #2
    Flow Master
    mr fantastic's Avatar
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    Quote Originally Posted by looi76 View Post
    Question:
    A car pulls a trailer with a force of 150N. This is shown in the diagram.

    (a) According to Newton's third law, forces exist in pairs.
    (i) What is the other force that makes up the pair?
    (ii) Write down the size and direction of this force?

    (b) The mass of the trailer is 190kg. As it sets off from rest, there is a resistive force of 20N.
    (i) Calculate the size and direction of the resultant force on the trailer.
    (ii) Calculate the initial acceleration of the trailer.

    (c) The force from the car on the trailer is maintained at 150N.
    When the car and trailer are traveling at constant speed.
    (i) What is the size of the resultant force on the trailer.
    (ii) Write down the size and direction of the resultant force on the trailer.

    Don't know how to start!...
    (a) The car and the trailer are the pairs?
    (a) The car pulls on the trailer (150 N to the left) therefore the trailer pulls on the car (150 N to the right).

    (b) Fnet = 150 - 20 = 130 N (to the left)
    Fnet = ma => 130 = (190)a => a = 13/19 m/s^2

    (c) Constant speed and unchanging direction => a = 0. Fnet = ma => Fnet = 0 N. (This would mean that the resisitive force on the trailer has increased to 150 N).
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