F(t)=19.84N.
When two bodies in contact move with respect to each other, rubbing the surfaces in contact, the friction between them is called kinetic friction.
Kinetic friction f_k=\mu _k \times N
where \mu _k is the coefficient of kinetic friction and N is the normal force.
Here the block will experience forces,
1) The normal force N in the upward direction
2) The gravitational force F=Mg in the downward direction
3) The tension T, say in the right direction
4) The kinetic friction f_k =\mu _k \times N in the left direction
For vertical equilibrium, N=Mg
We have kinetic friction f_k =\mu _k \times N=\mu _k \times Mg
As the block moves towards the right with an acceleration,
Total force on the block f_t_o_t_a_l=Ma=T-f_k
Ma= T- \mu \times Mg
T=Ma+\mu _k\times Mg
= M(a+\mu_kg)
=4×(3+ 0.2×9.8)
=19.84 N
The tension in the string is 19.84 N.
What are kinetic and static friction?
In static friction, the frictional force resists the force that is applied to an object, and the object remains at rest until the force of static friction is overcome. In kinetic friction, the frictional force resists the motion of an object.
Learn more about kinetic friction at
https://brainly.com/question/20241845
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