Forces at Work: Solving for the Magnitude of Resistance

[lim]

Homework Statement

A 21.7 g arrow is shot through a 9.6 cm apple. If the arrow enters the apple at 38.5 m/s and emerges witha speed of 31.2 m/s in the same direction, what is the magnitude of the force with which the apple has resisted the arrow?

Homework Equations

vf^2 = vi^2 +2adeltax
f= ma

The Attempt at a Solution

31.2^2 = 38.5^2 +2(9.6)a
973.44 = 1482.25 + 19.2a
a = -26.5
ma=|-575|
f= 575 N

 

[asd1249jf]

Homework Statement

A 21.7 g arrow is shot through a 9.6 cm apple. If the arrow enters the apple at 38.5 m/s and emerges witha speed of 31.2 m/s in the same direction, what is the magnitude of the force with which the apple has resisted the arrow?

Homework Equations

vf^2 = vi^2 +2adeltax
f= ma

The Attempt at a Solution

31.2^2 = 38.5^2 +2(9.6)a
973.44 = 1482.25 + 19.2a
a = -26.5
ma=|-575|
f= 575 N

Your method of calculation is correct. However, you need to watch out for the units. Convert them into proper units.

 

[lim]

So mass should be in kg, so .0217(-26.5) = |-0.575| = 0.575 N, but it still said it was wrong. Am I forgetting something else?

 

[asd1249jf]

So mass should be in kg, so .0217(-26.5) = |-0.575| = 0.575 N, but it still said it was wrong. Am I forgetting something else?

Yes. The size of the apple. Convert that into m.

 

[lim]

Oh! 57.51 N. Thanks for your help l46kok.