A 0.40 kg block rests on a desk. The coefficient of static friction is 0.20. You push the side of the block but do not have a spring scale to measure the force you use. The block does not move. Which statement is true about the force of static friction?
(Points : 3)
It is 0.08 N.

It is 0.78 N.

It is no larger than 0.78 N.

It is no smaller than 0.78 N.

Question

A 0.40 kg block rests on a desk. The coefficient of static friction is 0.20. You push the side of the block but do not have a spring scale to measure the force you use. The block does not move. Which statement is true about the force of static friction?
(Points : 3)
       It is 0.08 N.

       It is 0.78 N.

       It is no larger than 0.78 N.

       It is no smaller than 0.78 N.

anonymous · Answer

I need this done in 20 minutes, so if someone could help me that would be awesome.  i still have 3 more after this. :(

anonymous · Answer

would it be .08 because .40 and .20 multiplied is that?

surry99 · Answer

It is .78 because the F = mu x normal force
F = .2 x .4 kg x 9.8m/s^2 = .784 N

anonymous · Answer

Ok, that makes more sense, so no smaller than .78?

surry99 · Answer

It is precisely .78 no more no less.

anonymous · Answer

A baseball with mass of 0.145 kg is thrown straight down at the ground. At a particular speed, it has a drag force of 0.4 N acting on it. What is its acceleration at that time?
(Points : 3)
       9.8 m/s2

       2.8 m/s2

       12.6 m/s2

       7.0 m/s2

anonymous · Answer

What is the formula for this?

surry99 · Answer

Do you know what a free body diagram is?

anonymous · Answer

Yeah, it illustrates the forces acting upon an object, right?

surry99 · Answer

Yes...so mg acts downward you can calculate that..
but the drag of 4N acts upward so what is net force acting downward

surry99 · Answer

oops .4 N acts up

anonymous · Answer

Would the net force acting downward be gravity?

surry99 · Answer

not quite...here is what you have...
mg - drag = ma
.145 kg x 9.8 m/s^2 - .4 N = .145 kg x a...
now solve for a

anonymous · Answer

So it would be =7.04?

surry99 · Answer

Excellent!.  Does it make sense to you?

anonymous · Answer

Yes, thank you so much!

surry99 · Answer

you are welcome my friend

anonymous · Answer

I just have one left. A strong, weightless rope has a 0.15 kg mass hanging from the middle of it, as shown. What tension force will make the rope horizontal, corresponding to = 0°? http://gyazo.com/996dce41d55a5b4ef265583976802e12 (illustration) (Points : 3) 0.98 N 1.5 N 9.8 N No tension force can do this.

anonymous · Answer

the degree is 0 btw, the sign didnt transfer from my online homework

surry99 · Answer

No tension force can do this...There must be a vertical component to the tension to
oppose the weight which is acting opposite (downwards).  
Let me know if this makes sense to you

anonymous · Answer

That makes sense, yes

anonymous · Answer

Thanks for your help!  You are awesome!

surry99 · Answer

great! you are welcome and enjoy physics..it is great fun!