How much work is done by the crane in lifting the load?

[Sirsh]

Hi, i was just wondering with this question because I'm unsure if I am supposed to add both kinetic and gravitation energy into this answer? thanks.

1 A crane on a building site lifts an 8.00 × 102 kg load from ground level to a vertical height of 90.0 m at a constant speed of 2.00 m s–1. Ignore the mass of the cable.

A. How much work is done by the crane in lifting the load through this distance?
m = 800kg h = 90m g = 9.8ms^-2

E = mgh
E = 800*9.8*90
= 7.056*10^5 J

Sirsh.

 

[rock.freak667]

Hi, i was just wondering with this question because I'm unsure if I am supposed to add both kinetic and gravitation energy into this answer? thanks.

1 A crane on a building site lifts an 8.00 × 102 kg load from ground level to a vertical height of 90.0 m at a constant speed of 2.00 m s–1. Ignore the mass of the cable.

A. How much work is done by the crane in lifting the load through this distance?
m = 800kg h = 90m g = 9.8ms^-2

E = mgh
E = 800*9.8*90
= 7.056*10^5 J

Sirsh.

Yes you also need to add the kinetic energy

Total work done = PE+KE = constant at all points in the motion (this is the law of conservation of mechanical energy)

 

[Sirsh]

Are you sure? supposedly it's W = F/s therefore W = mg/s, W = 800*9.8/90 ??