Chapter SH, Problem 3.7APP

To determine

To Calculate: The force needed to lift mass.

Answer to Problem 3.7APP

  $245\text{N}$ (upwards)

Explanation of Solution

Given:

Mass of the object, $m=25\text{kg}$

Formula Used:

From Newton’s second law of motion, the net force would be:

  ${\displaystyle \sum F=ma}$

Here, m is the mass and a is the acceleration.

Weight of an object can be obtained by:

  $w=mg$

Here, g is the acceleration due to gravity.

Calculations:

At constant velocity, the acceleration of the object is zero. This means that the net force on the object is zero.

The forces acting on the object when it is being lifted are its weight acting in downward direction and the force exerted in the opposite direction to lift it.

  $\begin{array}{l}F+w=0\\ F=-w\\ F=-mg\\ F=-\left(\text{25kg}\right)\left(\text{9}{\text{.8m/s}}^{\text{2}}\right)\\ F=-245\text{N}\end{array}$

Conclusion:

Thus, the force needed to lift the object is $245\text{N}$ (upwards).