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physics

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A shopper pushes a grocery cart 20m at constant speed on level ground against a 35N frictional force. He pushes in a direction 25 degrees below the horizontal. What is the work done on the cart by gravity?

I know you can use W=Fdcos(theta) where F=mass*gravity. BUT, no mass is given so there must be some other way.

Help!

  • physics -

    gravity is doing no work because its perpendicular to the motion

  • physics -

    mass is not required. Constant speed means zero acceleration.
    Fcos(theta) - Ff=m*a
    Fcos(theta) - Ff=0
    F cos(25) =35
    0.9063F=35
    F=38.62N
    W=Fcos(theta)*d
    W= 38.62 cos(25)*20
    W=700J

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