Question

Force F is gradually increased from zero. Determine whether the block will first slide or lift up?

• A. slide
• B. lift
• C. won't move
• D. data insufficient

Answer 1

The correct option is A

slide

There are minimum magnitude of forces required both in horizontal and vertical direction either to slide or lift up the block. The block will first slide or lift up will depend upon which minimum magnitude of force is lesser. For vertical direction to start lifting up

F sin37${}^{\circ }$ + N$\ge Mg$

N Becomes zero just lifting condition.

F$\ge \frac{Mg}{sin{37}^{\circ }}$

$F_{lift}\ge \frac{10g}{3/5}$ $\therefore F_{lift}\ge \frac{500}{3}N$

For horizontal direction to start sliding

Fcos37${}^{\circ }$$\ge$${\mu }_{s}N$

Fcos37${}^{\circ }$ > 0.5[10g-Fsin37${}^{\circ }$] ($\because$ N =10g-Fsin37${}^{\circ }$)

Hence $F_{slide}$>$\frac{50}{cos{37}^{\circ }+0.5sin{37}^{\circ }}$

$F_{slide}$>$\frac{500}{11}N$

$F_{lift}$ > $\frac{500}{3}N$ $\Rightarrow F_{slide}$< $F_{lift}$

Therefore the block will begain to slide before lifting.