How Do I Calculate Friction Force and Mass in This Dynamics Problem?

[physics_newb]

Dynamics Problem..Grade 11 Urgent Help Needed!

Homework Statement

Paul and Mintu are attempting to push a heavy fridge across the kitchen floor. When Paul pushes it with a muscular force of 550N, the fridge accelerates from rest to 28.0cm/s in 3.5s. When Pintu pushes it with a muscular force of 560N, the fridge accelerates from rest to 36cm/s in 3.0s. Calculate the force due to friction and mass of the fridge.

Homework Equations

v1=0.0cm/s
v2=28.0cm/s
t=3.5s
F=550.0N
F_2=?
a=?

The Attempt at a Solution

Paul
v1=0.0cm/s
v2=28.0cm/s
t=3.5s
F=550.0N
F_2=?
a=?

Step 1
a=(v_2-v_1)/t
a=(28-0)/3.5
a=28/3.5
a=8m/s^2
Step 2
Fnet=ma
F_net=F+F_2
ma=F+F_2
Type equation here.



That is what I've done so far but after I got to the end of that I realized mass wasn't given and now I'm totally confused as the teacher didn't give us any notes on how to deal with this! Please help me solve this I am completely confused
Thanks

 

[rl.bhat]

You have two equations. One due to Paul and the other due to Mintu. In both the case F_2 is the same. Solve the two simultaneous equations to find m and F_2.

 

[physics_newb]

I'm sorry, I do not follow I realize that there are 2 equations and F2 should be the same but I do not understand how I use those 2 F1's to get F2 and mass. Would it be possbile to please explain further/more detail...I am completely clueless

 

[physics_newb]

can anyone please help me with this its 11pm here and this is due first thing in the morning and right now I'm clueless on how to do it

 

[rl.bhat]

OK.
For Paul
m*a1 = 550 N + F_2 -----(1)
Fro Pintu
m*a2 = 560 N + F_2 -----(2)
You have found a1. Now find a2. Substitute these values in eq.1 aand 2. Subtract eq.2 from eq.1 and find m. Then using anyone of the equation finf F_2.

 

[physics_newb]

ohhh we have to use substitution to find m...and then find f2 using the rest? Thanks! I think i just kind of went mind blank there for a moment

 

[physics_newb]

ok I am kind of stuck again...after I got f2=-530N, the mass makes no sense...after solving it seems that mass =2.5...would it be 2.5 tonnes? kg? g? or is there something i did wrong?
Step 1 (Paul)
v1=0.0cm/s
v2=28.0cm/s
t=3.5s
F =550.0N
F_2=?
a=?

a=(v_2-v_1)/t
a=(28-0)/3.5
a=28/3.5
a=8m/s^2




Step 2 (Mintu)
v1=0.0cm/s
v2=36.0cm/s
t=3.0s
F =560.0N
F_2=?
a=?

a=(v_2-v_1)/t
a=(36-0)/0
a=36/3
a=12m/s^2
Step 3 (Substitution)
Fnet=ma
Fnet=F+F_2


m*8=550+F_2
m=(550+F_2)/8


m*12=560+F_2
m=(560+F_2)/12

Substitution
m=(560+F_2)/12→m=(550+F_2)/8
(560+F_2)/12=(550+F_2)/8
560+F_2=(550+F_2)/8*12
560+F_2*8=550+F_2*12
4480+8F_2=6600+12F_2
8F_2-12F_2=6600-4480
-4F_2=2120
F_2=-530N
Sub for equation 1
m=(550+F_2)/8
m=(550+(-530))/8
m=20/8
m=2.5

 

[physics_newb]

NVM I realized what i was doing wrong...i was using 8 (cm/s/s) instead of 0.08 (m/s/s)