Physics

posted by Riley

A bar with a mass of 20kg with a length of 30m is being lifted by a string and makes an angle of 55 degrees. The string is attached to the ceiling vertically.
What is the tension on the string?
What is the normal force given by the bar on the string
what is the force of static friction given by the ground on the bar?

1. Damon

Where does the string attach to the rod?
What on earth do you mean by normal force on a string? Strings are usually in tension.

2. Damon

55 degrees with what?

3. Riley

*30cm bar
*55 degrees above the horizontal between the rod and the ground
*normal force given by the bar and the ground

4. Riley

*string is attached to one end of the string while other end is on the ground

5. bobpursley

sum of moments is zero. summing moments about the origin at the ground

20kg*9.8*15cm -Tension*length*sin(90-55)=0
that assumes the string is vertical at the point "length". if on the end, length-30cm.
Solve for tension.
<what is the normal force given by the bar on the string?> the negative of tension.
<static friction?>
The bar will tend to rotate about where the string is attached.

static -friction*length*sin55+verticalforceonground*length*cos55 + lenght/2*20*9.8=0 (moments in clockwise are negative, counterclockwise +)
Vertical force on ground=20kg*9.8-Tension
solve for friction

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