Question

An ideal spring fixed from left end, of spring constant $5N/m$ is attached to a block and is stretched to a distance $3m$ from relaxed position towards right end. If the block compresses to half of its initial extension after release, what is the average frictional force?

• A. $4.25N$
• B. $3.75N$
• C. $2.75N$
• D. $2.5N$

Answer 1

The correct option is B $3.75N$

k= 5 N/m, $x_1=3m$

$\Rightarrow$ every $v_1=\frac{1}{2}k{x}^2=22.5$ joule

compresses =$\frac{3}{2}$=$1.5m=x_2$

$\Rightarrow$every =$v_2=\frac{1}{2}k{x}^2=1.125\times 5$

=5625 joule

lose = 22.5-5.625 = 16.875 joule

distance = 3m right +1.5 (compression)

(in coming to real x)

=4.5

Force $\times 4.5=16.875$ joule $\Rightarrow$ force $=\frac{16.875}{4.5}=3.75N$