Question

You push really hard against a round rock, but you cannot make it roll. Which statement best explains why you cannot move the rock?

Gravity pulls the rock toward the center of Earth.
The forces between you and the rock are balanced.
The force of your push is greater than the opposing force.
There is no friction to help you move the object.

Answer 1

Given:

You push really hard against a round rock, but you cannot make it roll. Which statement best explains why you cannot move the rock?

• Gravity pulls the rock toward the center of Earth.
• The forces between you and the rock are balanced.
• The force of your push is greater than the opposing force.
• There is no friction to help you move the object.

Diagram:

Consider the rock to be a cuboidal block placed on the ground.

$\setlength{\unitlength}{1mm}\begin{picture}(5,5)\put(0,0){\framebox(15,15){\sf{M}}}\put(-20,-0.1){\line(1,0){55}}\multiput(-19,0)(3,0){19}{\qbezier(0,0)(-1,-1)(-2,-2)}\put(15,7.5){\vector(1,0){15}}\put(7.5,0){\vector(0,-1){15}}\put(4,-20){\sf{Mg}}\put(7.5,15){\vector(0,1){15}}\put(6.3,31.5){\sf{N}}\put(0,0.2){\vector(-1,0){15}}\put(-17,1.3){\sf{f}}\put(32,6){\sf F}\end{picture}$

• Here F is the applied force, f is the friction , Mg is the weight of the body and N is the normal reaction.

Solution:

When you are trying to push the rock in a static conditions , static friction opposes the applied force.

Static friction is a self - regulating opposing force which increases with increase in applied force upto a critical limit.

Since the weight of rock is huge, the critical limit is also large in value. Hence, we need to apply a large amount of force to reach the critical limit.

Till then, the applied force is balanced with friction.

And hence the block doesn't move.

CORRECT STATEMENT:

The forces between you and the rock are balanced.

Answer 2

Answer:

The forces between you and the rock are balanced.

Explanation:

NONE!!!