A crane lifts a 425 kg steel beam vertically upward a distance of 78 m. How much work does the crane do on the?

A crane lifts a 425 kg steel beam vertically upward a distance of 78 m. How much work does the crane do on the beam if the beam accelerates upward at 1.8 m/s^2? Neglect Frictional forces.
I feel like you can’t add the accelerations, you’d have to subtract because they’re in opposite directions.

3 Responses to “A crane lifts a 425 kg steel beam vertically upward a distance of 78 m. How much work does the crane do on the?”

  1. bonobo  on August 26th, 2012

      Work = PE gained = m • g • h

                     = (425 Kg) • (9.8 m/sec²) • (78 m)

                     = 324870 Joules

    Reply

  2. glo :D  on August 26th, 2012

    I don’t know if this is the right answer, but I used W = N x m. So (425 x 9.8 m/s^s) x (78m), would give you work…but it doesn’t seem right because I didn’t use the acceleration.

    . maybe you can use F = ma.. then.. (425 kg x 1.8 m/s^2) would give you force.. then use that F for W = N x m..( the answer to F x 78m)..?

    I hope this doesn’t confuse you.. hehe.

    Reply

  3. James  on August 26th, 2012

    Use Newton’s second law

    F=ma
    F-mg=ma
    F=ma+mg
    F=m(a+g)

    Since Work Done=Force x Distance
    W=m(a+g) x d
    so
    W=md(a+g)
    W=(425)(78)(1.8+9.8)

    Reply


Leave a Reply