Question

A man picks up an object of mass 4kg and lifts it 5m. He then moves forward 3m.

Answer 1

a) 39.2 N

b) Upwards

c) 196 J

d) 0 J

EXPLANATION

a) The minimum force required to pick up an object from the ground is the force that equals the sum of the forces in the opposite direction:

We want to pick the object up, so the minimum force required to do that is the weight of the object Fg:

`F_g=m\cdot g`

m is 4kg and g = 9.8 m/s²:

`F_g=4kg\cdot9.8m/s^2=39.2N`

b) As said in item b, to lift the object we want to apply the force upwards.

c) The work W needed to move an object a distance d with force F is:

`W=F\cdot d`

The force is the one found in item a of this problem, F = 39.2N. The distance is the height the man lifted the object: d = 5m:

`W=39.2N\cdot5m=196J`

d) When the man moved forward he was already holding the object, so he and the object moved together. Therefore there's no 'extra' force applied on the object and the work done by the man on the object is zero.