Question

The cable of a crane is lifting a 950 kg girder. The girder increases its speed from 0.25 m/s to 0.75 m/sin a distance of 5.5m

Answer 1

Explanation:

a) How much work is done by gravity?

• w = f x d
• w = 950 x 10 x 5.5 = 52250j

b) How much work is done by tension?

• v²=u²+2as
• 0.75²=0.25²+2a x5.5
• 0.56=0.06+2a x5.5
• 2a x5.5 = 0.56 - 0.06
• 2a x 5.5 =0.5
• 11a=0.5
• a = 0.5/11 = 0.05m/s²

w = f x d

w = 950 x 0.05 x 5.5 = 261.25j