Chapter 2, Problem 21A

Blocks A and B are supported by the table. Block C is partly supported by the table and partly by the rope. Rank the support forces provided by the table from greatest to least.

To determine

To rank: The support forces provided by the table from greatest to least.

Answer to Problem 21A

All will have equal force.

  $F_A=F_B=F_C$

Explanation of Solution

Introduction:

Equilibrium is basically a state of no change in the object. Thus, if the object is in equilibrium, then the net force on it is zero, that is,

  ${\displaystyle \sum F}=0$

Now, when the blocks rest on a table, then net force on it zero.

Consider the figure shown below.

  

For the case A and B, the support force on the blocks must be balanced by the weight of the blocks which is same for both the cases. Thus,

  $F_{\text{support}}=W_{\text{block}}=10\text{N}$

But for case C, an upward force of $10\text{N}$ acts on the block. Thus, net force on it can be written as,

  $\begin{array}{c}{W}_{\text{block}}=F_{\text{support}}+10\text{N}\\ F_{\text{support}}=20\text{N}-10\text{N}\\ \text{=10}\text{N}\end{array}$

Conclusion:

Hence, the support forces on the given blocks will be same and is given by $F_A=F_B=F_C$ .