Question

You do 30 J of work to load a toy dart gun. However, the dart is 10 cm long and feels a frictional force of 10 N while going through the dart gunâs barrel. What is the kinetic energy of the fired dart?
a. 30 J
b. 29 J
c. 28 J
d. 27 J

Answer 1

Answer: Option (b) is the correct answer.

Explanation:

The given data is as follows.

         $K.E_{1}$ = 30 J,    l = 10 cm = 0.1 m (as 1 m = 100 cm)

               F = 10 N  

The formula to calculate the work done is as follows.

          W = $F \times l$

Hence, putting the given values into the above formula as follows.

                W = $F \times l$

                     = $10 N \times 0.1 m$

                     = 1 J

As the dart loses 1 joule of energy when it goes through the barrel. Therefore, the kinetic energy it has when it comes out is calculated as follows.

              K.E = 30 - 1

                    = 29 J

Thus, we can conclude that the kinetic energy of the fired dart is 29 J.

Answer 2

Answer: Option (b) is the correct answer.

Explanation:

The given data is as follows.

= 30 J, l = 10 cm = 0.1 m (as 1 m = 100 cm)

F = 10 N

The formula to calculate the work done is as follows.

W =

Hence, putting the given values into the above formula as follows.

W =

=

= 1 J

As the dart loses 1 joule of energy when it goes through the barrel. Therefore, the kinetic energy it has when it comes out is calculated as follows.

K.E = 30 - 1

= 29 J

Thus, we can conclude that the kinetic energy of the fired dart is 29 J.