Question

A block of mass $1kg$ lies on horizontal surface in a truck. The coefficient of static friction between the block and the surface is ${\mu }_s=0.6$. If the acceleration of the truck is $5m/s^2$, the friction force acting on the block is

• A. $4\text{N}$
• B. $5\text{N}$
• C. $6\text{N}$
• D. $7\text{N}$

Answer 1

The correct option is B $5\text{N}$

Let us assume the truck has acceleration in the righttward direction. The FBD of the block in the frame of truck can be shown as

From the FBD we have
$N=1g=10\text{N}$
$f_{max}=\mu N=10\mu =10\times 0.6=6\text{N}$
Applying the concept of pseudo force in the frame of truck,
the force on the block is
$ma=1\times 5=5\text{N}$
Since, $f_{max}>ma$, the friction force acting over the block is $f=ma=5\text{N}$