Physics 12U - 5 Force Problems

[umaza]

Physics 12U - 2 Force Problems

Homework Statement

See attachment.

I am very confused with these two questions.

Question 1: I understand how to do the pulley. Would the force the guy at the top is being pulled at be the same as the force with which the guy needs to push with? How does a horizontal push stop something from falling?

Attempt:
F_netJOE = F_t, F_netBRIAN = -F_t + F_gBRIAN.
a₁ = m_BRIAN*g / (m_JOE + m_BRIAN)
a₁ = 4.2m/s/s

F_t = m_JOE*a
F_t = 336N

I get stuck here, would the push require the same force as tension or same acceleration? Any hints?
Also why does it matter about the mass of the pusher (JOE)?

This part below I do not know if it is right or not (equal accelerations):
The pusher must accelerate the box at 4.2m/s/s, the mass is equal to the total mass of box + the two others in contact.

F_net = m_{Box+John+Brian}*a
F_net = 588N

Question 2: I do not understand at all. How does a horizontal force lift something vertically?

Attempt:
F_gB = m_B*g
F_gB = 980N

This part below I do not know if it is right or not:
For the barrel to move up, it needs a force of 980N+, but for minimum I stick to 980N.

Where the pipe touches the Barrel is 0.25m of the ground. From this point I make a triangle from point of contact to middle, being 1m (diameter = 2m), I treat this as hypotnuse and 0.75m as opposite side. From this I get an angle.

θ = sin^-1(1/0.75)
θ = 48.6°

Now I use this angle with the vertical component being 980 (opposite side), and find horizontal component.

adj = 980 / (tan48.6)
adj = 864N

 

[SammyS]

Homework Statement

See attachment

I am very confused with these questions.

Question 1: I understand how to do the pulley, but when I get its acceleration it is 4.2m/s/s, but then the force of tension is different. Would the force the guy at the top is being pulled at be the same as the force with which the guy needs to push with? How does a horizontal push stop something from falling?

Question 2: I do not understand at all. How does a horizontal force lift something vertically?

Question 3: I get how the weights are different, but after that I am stuck. Would they have constant velocity?

Question 4: I am having troubles with drawing the FBD and how does the incline affect the weight when the person is on a horizontal surface?

Question 5: The force he pulls with must be half of gravity because he is aided when he pushes down on the rope, but would he pull down on 20m of rope or would he pull on 40m of rope?

Hello umaza. Welcome to PF !

You might have better luck posting only one or two questions per thread. (That's a rule for this Forum.)

Also, you need to be more detailed about your progress toward solutions so we can give more meaningful responses.

 

[umaza]

Thanks, it is great to be here.

The problem is that I do not know where to start I am really stuck. What I was looking for was really an explanation of the concepts and to know where to start. All other homework questions I was given I did with ease, but with these problems I am finding there is too little information.

The only formula that comes to mind for these questions is F = ma.

And about how many questions, did you mean only 1 to 2 problems or 1 to 2 help questions.

Thanks for advice, I got rid of three questions and have listed one attempt for both.

 

[umaza]

Anyone? Should I post the actual question on post?

 

[asteriatic]

Hello,

As a scientist, my first suggestion would be to carefully review the concepts of forces and Newton's laws of motion. In the first question, it is important to understand that the force exerted by the person pushing the box (JOE) is not the same as the tension in the rope (Ft). The force exerted by JOE is what causes the acceleration of the box, while the tension in the rope is what keeps the box from falling due to gravity.

To answer your first question, the person at the top of the pulley is being pulled up with a force equal to the tension in the rope (Ft). However, the force with which the person must push to accelerate the box is different and can be calculated using Newton's second law, F = ma. The mass of the pusher (JOE) does not matter in this case because it is being cancelled out in the equation.

In the second question, the key concept to understand is that forces can act in different directions and still have an effect on an object. In this case, the horizontal force is acting in the same direction as the vertical force of gravity, causing the object to move upward. This can be explained by considering the components of the forces in different directions. The horizontal force is being applied at an angle, so it has both a horizontal and vertical component. The vertical component is what contributes to the upward motion of the object.

To solve the problem, you correctly used the trigonometric functions to find the horizontal component of the force. However, it is important to note that this is the minimum force required to lift the object. The actual force needed may be greater depending on factors such as friction.

In summary, it is important to have a solid understanding of the fundamental concepts of forces and Newton's laws of motion in order to successfully solve these problems. I would suggest reviewing these concepts and practicing with similar problems to improve your understanding. Additionally, don't hesitate to seek help from a teacher or tutor if you are still struggling. Good luck!