Question

5. The body, weighing 4kg, rises at a constant speed v = 2 m / s, under the action of a constant force F. Find the force of force F, as well as the work performed by it during 2s.

Answer 1

Since the speed of the body is constant, the force $F$ should be equal and opposite to the weight of the body. Thus:

$$F = mg$$

where $m = 4kg$ is the mass of the body, and $g = 9.8m/s^2$ is the gravitational acceleration.

The power of this force is then:

$$P = Fv = mgv$$

where $v = 2m/s$ is the speed of the body.

And the work is:

$$W = Pt = mgvt$$

where $t = 2s$ is the time. Thus, obtain:

$$P = 4\cdot 9.8\cdot 2 = 78.4W$$ $$W = 4\cdot 9.8\cdot 2\cdot 2 \approx 157J$$

Answer. Power: 78.4W, Work: 157J.