# Newton's Second law

1. Oct 10, 2015

### Igniuxx6

1. The problem statement, all variables and given/known data
Influenced by certain force, cart moved from place and driven 0.5 meters distance. When 200grams weight was placed on cart it moved 0.3 meters during the same period of time. Calculate the mass of the cart.

2. Oct 10, 2015

### Daeho Ro

So, how did you tried?

3. Oct 10, 2015

### Igniuxx6

Tried to get acceleration by converting grams to kilos, then dividing 0,3 meters with 0,2 kilos. Got 1,5, but I doubt its right. If 1,5 would be correct, I would just use ΣF⃗=ma⃗

4. Oct 10, 2015

### Daeho Ro

Then, why do you need the acceleration? I know you want to use the Newton's second law, but there are many missing parameters to use this.

5. Oct 10, 2015

### Igniuxx6

I want acceleration to get force and with Force + Acceleration I would get mass. So what I should use instead? Pretty lost,

6. Oct 10, 2015

### Daeho Ro

In this statement, I can get the velocity of cart and cart + 200grams weight, roughly. But I don't know how to get the acceleration.

7. Oct 10, 2015

### Igniuxx6

How about a1=V1-V01/t a2=V2-V02/t that leads to (V1-V01)*t/t*(V2-V02), we cancel out t and we get (V1-V01)/(V2-V02), now I need to know how you get velocity of cart and cart + 200grams.

8. Oct 10, 2015

### ehild

You know the displacements. Assuming uniform acceleration, how is the displacement related to time and the acceleration?

9. Oct 10, 2015

### Igniuxx6

Displacement moves same distance each time interval

10. Oct 10, 2015

### Daeho Ro

What you means is the constant velocity. Is this problem settle down with constant acceleration or constant velocity?

11. Oct 10, 2015

### Igniuxx6

You mentioned you are abble to get velocity, if you would tell me how, I (maybe) would be abble to get acceleration from there and use it to get mass.

12. Oct 10, 2015

### Daeho Ro

I supposed the cart moves without acceleration, that is constant velocity. Since we know the displacement within unknown time interval $T$, I can only tell you that the velocity is in a form $0.5 m / T$.

13. Oct 10, 2015

### ehild

The problem statement is:
If a certain force takes place, the velocity is not constant.

14. Oct 10, 2015

### Daeho Ro

I thought the certain force only acted at the initial and the cart moves freely. But, it seems you are right. My poor English sometimes confuse me.

15. Oct 10, 2015

### Daeho Ro

Ok, then now I am clear.

The cart with mass $M$ and cart + weight with mass $M + m$ moved by a fixed certain force $F$ and the displacements are $d_1$ and $d_2$, respectively.

16. Oct 10, 2015

### ehild

That is true now.
But this is Igniuxx6's thread. Do not confuse him, and do not try to solve his problem. Both are against the rules of these Forums.

17. Oct 10, 2015

### Igniuxx6

So
m2=0,2kg
m=m1+m2
F=d1+d2/m2=0,5+0,3/0,2=4N
a=F/m2=20
m1=F/a=4/20=0,2kg
m=0,2+0,2=0,4kg

18. Oct 10, 2015

### Daeho Ro

In constant acceleration, the displacement is well known and because we know the displacement, you can get the acceleration.

This part is really strange. Why don't you check the relevant equations?

19. Oct 10, 2015

### Igniuxx6

So its like a=9,8?
So it would be :
F=m*a=0,2*9,8=1,96N
m1=F/a=1,96/9,8=0,2kg
m=0,2+0,2=0,4kg?

20. Oct 10, 2015

### Daeho Ro

For example, the displacement with constant velocity is given by $d = v t.$ What about the displacement with constant acceleration?