Question

How much work is required to lift an object with a mass of 5.0 kilograms to a height of 3.5 meters?

a. 17 joules
b. 1.7 × 102 joules
c. 1.9 × 102 joules
d. 2.8 × 102 joules

Answer 1

B. 1.7 × 10^2 joules

Answer 2

Hello there.

This problem is algebraically simple, but we must try to understand the 'ifs'.

The work required is proportional to the force applied and the distance between the initial point and the end. Note: the work does not take account of the path which is described by the object, only the initial and final point. This happens because the gravitational force is generated by a conservative vector field.

Assuming the ascent speed is constant:

The force applied equals to the weight of the object. Then:

F = W = m . g

F = 5 · 9,81

F = 49,05 N

Since work equals to Force times displacement in a line, we write:

`\tau = F\cdot d = mgh = W\cdot h\\ \\ \tau = 49.05\cdot3.5\\\\\tau = 172~J\approx 1.7\cdot10^2~J`

Letter B