Calculating Mass on a Frictionless Surface

  • Thread starter Hawk_RSA
  • Start date
  • Tags
    Newtons
In summary, the conversation is about calculating the mass of an object on a frictionless surface that is being pulled along a horizontal line with a string that has no mass. The answer provided is 17.1 kg, but the person is unsure about the steps to get to that answer. Two possible solutions are provided, one involving finding the acceleration of the 15 kg mass and using it to solve for the unknown mass, and the other involving setting up an equation using the net force and the individual forces on the system. Both solutions result in a mass of 17.1 kg.
  • #1
Hawk_RSA
3
0
http://img75.imageshack.us/img75/9735/prob1ve7.jpg

Frictionless surface, pulled along a horizontal line, string has no mass

Calculate the mass m


The answer says 17,1 kg, i don't know if it is correct,
can sum1 please give a solution with the steps:smile:
 
Last edited by a moderator:
Physics news on Phys.org
  • #2
The answer is correct. You have to show some work for us to help you.
 
  • #3
I don't know how to put it.

I can work out the force of the string and the accel but i can't do it the other way around

i have taken the answer and tried to work backwards and see if i get 80N force on the sting between the block

For block m (17,1 kg's)

Fr = ma
F2 = 17,1a

For 15 kg mass

Fr = ma
150 - F1 = 15a
F1 = 150 - 15a

Newton's 3rd law F1=F2

150 - 15 = 17,1a

32,1 a = 150
a = 4,67289..

F = ma
F = 17,1 * 4,67289..
F = 79,906..
F = 80 N

so the answer is correct, but i can't seem to work out the mass
I don't know where to start,

I don't know how to get the acceleration:confused:
 
  • #4
Have you tried drawing the free body diagram for the 15 kg mass?
 
  • #5
You calculate the acceleration by isolating the 15 kg mass, and taking into consideration the applied force and the tension force.
Fnet = Fapp - Ft
ma = 150 - 80
15a = 70
a = 4.67
 
  • #6
Now to find the unknown mass, you have to use the entire free body diagram. This time you have to ignore the tension force.

Fnet = Fapp
ma = 150
(15 + m)(4.67) = 150
(15 + m) = 32.1
m = 32.1 - 15
m = 17.1 kg
 
  • #7
You must first isolate the 15 kg mass and find its acceleration. So now, you can use this value to determine the mass of the unknown mass.
 
  • #8
Thanks guys
this is the other sullution i got:
F = ma
a = F/m
call the object of mass 15kg object 1
call the object of mass m kg object 2
acceleration of system (object 1 + object 2) = acceleration of object 1 = acceleration of object 2 = 150N / (15kg + m kg)
acceleration of object 2 = 80N / m kg
therefore:
150 / (15 + m) = 80 / m
multiply through etc
1200 + 80m = 150m
1200 = 70m
m = 17.14
 

FAQ: Calculating Mass on a Frictionless Surface

What are the three laws of motion in Newton's laws?

The three laws of motion in Newton's laws are: (1) an object at rest will stay at rest and an object in motion will stay in motion with a constant velocity unless acted upon by an unbalanced force (Newton's First Law), (2) force equals mass times acceleration (Newton's Second Law), and (3) for every action, there is an equal and opposite reaction (Newton's Third Law).

How do Newton's laws apply to everyday life?

Newton's laws can be seen in everyday life in various ways. For example, when a car accelerates, the passengers feel pushed back into their seats because of Newton's First Law. In addition, when you throw a ball, the force of your hand pushing the ball forward is the same as the force of the ball pushing back against your hand, as described in Newton's Third Law.

What is the difference between mass and weight according to Newton's laws?

Mass is a measure of the amount of matter in an object, while weight is a measure of the force of gravity acting on an object. According to Newton's laws, mass is a constant property of an object and does not change, while weight can vary depending on the strength of the gravitational force acting on the object.

How can we apply Newton's laws to understand the motion of objects?

To understand the motion of objects, we can use Newton's laws to analyze the forces acting on the object and the resulting acceleration. By knowing the mass and forces acting on an object, we can use Newton's Second Law to calculate the acceleration of the object. From there, we can use Newton's First Law to predict the motion of the object if there are no unbalanced forces acting on it.

Can Newton's laws be applied to objects in space?

Yes, Newton's laws can be applied to objects in space. In fact, they were initially developed to explain the motion of celestial bodies in space. Newton's laws still apply to objects in space, but the forces acting on them may be different due to the absence of air resistance and the effects of gravity from other objects in space.

Similar threads

Newton's law problem: Pushing 2 stacked blocks on a horizontal table
Replies
13
Views
2K
Distribution of Energy when work is done on a system of 2 masses connected by a spring
Replies
17
Views
601
Ideal Vs Real Mass Pulley system
Replies
10
Views
4K
A mass is free to move on a horizontal frictionless surface
Replies
10
Views
5K
A system comprising blocks, a light frictionless pulley, and
Replies
6
Views
3K
Solve Pulley-Mass System: m1=4.00 kg, m2=1.00 kg
Replies
2
Views
1K
Tension in a string between two blocks
2
Replies
45
Views
23K
Newton’s Law of Motions: tension forces in a pulley
Replies
4
Views
1K
Impossibility of unforced movement on a frictionless surface
Replies
1
Views
1K
Masses connected by a pulley on a frictionless surface
Replies
9
Views
14K

Hot Threads

Recent Insights

Back
Top