Question

a bullet having mass 10g is fired towards a fixed wooden block with velocity of 30m/s. it comes out of the block with velocity of 20m/s then the total work done by the resistive force is.

1)-4.5j
2)2j
3)-2.5j
4)0​

Answer 1

Explanation:

first using

V²-u²=2as

we get S= 25 m

then

for a

v²-u²=2as

v²-0 =2as

a =v²/2s

we get a= 18 m/s²

then F =ma

F=10×10^-3 ×18

F=180×10^-3

then

Work done =F×d

=180×10^-3×25

=4500×10^-3 J

=4.5 J

because it is resistive it will be negative therefore answer will be -4.5J

Answer 2

Given: A bullet having mass 10g is fired towards wooden block with 30m/s and comes out with 20m/s

To find: Work done by resistive force

Explanation: Mass(m)= 10g = 0.01 kg

Now, final velocity (v)= 20m/s

Initial velocity (u) = 30m/s

Using law of motion,

$\frac{{v}^{2} - {u}^{2} }{2} = as$

where a is acceleration and s is distance

=> as= (400-900)/2

=> as= -250

Resistive force= mas

= 0.01*-250

= -2.5 J

Therefore, the resistive force is equal to -2.5 J.