physics

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speed of the car is 47.52 km/hr. a lorry wheel is rotating at 400 RPM. what is the radius (in cm) of a lorry wheel if the lorry has a same speed with the car?

  • physics -

    since car and lorry wheel has same speed
    so
    kinetic energy of car = rotational energy of lorry wheel
    1/2mv^2= 1/2mw^2r^2
    v= r w
    where
    w= rotational velocity
    r= v/w=13.2/41.8=0.31 m= 31.5 cm

  • physics -

    I disagree.
    The speed of a point on the outer edge of the lorry wheel is 47.52 km/hr

    angular velocity =
    400 * 2 pi radians/60 seconds
    speed = angular velocity * R
    so
    (400* 2/60) pi R = (47.52*10^3/3600)meters/second

  • physics -

    I don't see any disagreement. Both previous responders use V = R*w.
    Tarun has already correctly converted V to m/s and w to rad/s. (Actually, I get 41.88 rad/s for w).

    The land speed of a point on a rolling wheel depends upon the location. It equals V (vehicle velocity) at the axle, 0 at the point of contact with the ground (the "instant center" of rotation) and 2V at the top edge of the tire.

  • physics -

    I disagree that the kinetic energy of the car is equal to the kinetic energy of the lorry wheel :)

  • physics -

    I agree with Damon's last statement about kinetic energy.

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