Two blocks are being pushed across a horizontal floor with a coefficient of kine
ID: 1596677 • Letter: T
Question
Two blocks are being pushed across a horizontal floor with a coefficient of kinetic friction m=.3 . The mass of block A is 3kg, and the mass of block B is 2 kg.
I.) If the force being applied by the finger is F, what is the force that block A applies to block B?
a. FAonB = F
b. FAonB = F/2
c. FAonB = 2F/5
II.) If the force applied by the finger is F=20N, what is the acceleration of the blocks?
a. a = .68 m/s2
b. a = .94 m/s2
c. a = 1.06 m/s2
III.) If the force applied by the finger was doubled, the acceleration of the blocks would be:
a. less than twice as much
b. exactly twice as much
c. more than twice as much
Explanation / Answer
mA=3kg and mB=2kg
co-efficient of kinetic friction u=0.3
1)
force equation for mass mA,
mA*a=F-F_AB-u*mA*g
3*a=F-F_AB-0.3*3*g
3*a=F-F_AB-0.9*g ---(1)
and
force equation for mass mB,
mB*a=F_AB-u*mB*g
2*a=F_AB-0.3*2*g
2*a=F_AB-0.6*g --(2)
from equation no (1) and (2),
3/2=(F_FAB-0.9*g)/(F_AB-0.6*g)
3*F_AB=2*F-2*F_FAB
5*F_AB=2*F
===> F_AB=2*F/5
b)
from equation no (2)
2*a=F_AB-0.6*g
2*a=2*F/5-0.6*g
2*a=2*20/5-0.6*9.8
====> a=1.06 m/sec^2
c)
the correct oprion is (C) more than twice as much