Quiz 1: Testing Your Knowledge of Force & Inertia

[Ab e r z o m]

http://physicsed.buffalostate.edu/c...anics/PDF files/4-FP-Inertia/Tests/Quiz 1.pdf

1) I don't know how to do this, but I know there is the force of gravity by the Earth in the force diagram..

2) For this one I got the answer
Fx=7.5N [I did 1/2(15N) which equals 7.5 N]
Fy=13N [I took my x component 7.5N and I did 7.5sqrt3=13N]
Did I solve this problem right??

3) How do you write an equation for this diagram?

Can you tell me if I did the Bonus right?

T1cos(60)=T2
T2sin(60)= 3kg

T1sin(60)=3kg
I divided both sides by sin(60) to make T1 by itself so
T1sin(60)/sin(60)=3.464
SO T1=3.464

I took T1=3.464 and plug it into T1cos(60)=T2
3.464cos(60)=T2
T2=1.232

So I don't know if I got that one right??
My answer is T1=3.464 and T2=1.232

Please help me..I really need this. Thank you!

 

[phyzmatix]

1) There is also a normal force and a kinetic frictional force.
2) You need to resolve your vector into components using trig.
3) The system seems to be in equilibrium, so

$$F_{xnet}=0$$

and

$$F_{ynet}=0$$

Start from there and re-think your strategy for the bonus part. For one, tension is a force so you can't measure it in kg...Remember Newton's second law.

 

[thomate1]

I can confirm that your calculations for questions 1 and 2 are correct. You correctly identified the force of gravity as the downward force in the force diagram and used the correct equations to find the components of the force.

For question 3, to write an equation for the diagram, you can use the formula for Newton's Second Law: F=ma. In this case, the force (F) is the tension in the rope (T) and the mass (m) is 3kg. So the equation would be T=3kg*a.

For the bonus question, your calculations are mostly correct. However, for T1cos(60)=T2, you should use the value of T1 that you calculated earlier (3.464), not the sin(60) value. So the correct equation would be 3.464cos(60)=T2. And your final answer for T2 should be 3.464, not 1.232.

I hope this helps and clarifies any confusion. Keep up the good work in your studies of force and inertia!