# Finding mass

by 2much
Tags: mass
 P: 14 1. The problem statement, all variables and given/known data You apply a force of .35N up to lift a fork, the resulting acceleration is .15m/s2. What is the mass in grams. Please help I don't know where to start with this simple question.
 Sci Advisor HW Helper PF Gold P: 5,920 Start with identifying the net force acting on it, and use Newton's 2nd law. Please show an attempt.
 P: 14 The net force would not be zero and I am only given the applied force. Without a mass I don't know how I can get the force of gravity. So as far as I can tell I have .35 Fg = m .15m/s2
Emeritus
HW Helper
PF Gold
P: 7,246

## Finding mass

Let mass = m & use symbols where needed.

What does Newton's 2nd Law say?
 P: 14 0.35 Fg = m .15m/s2 0.35 - (m 9.8 m/s2) = m 0.15ms2 The second law says that if the net force is not zero there is an acceleration in the direction of the force.
 Emeritus Sci Advisor HW Helper PF Gold P: 7,246 You apply a force of 0.35 N upward. If the mass of the for is m, what force is gravity exerting downward on the fork? What is the net force being exerted upon the fork?
 P: 14 Wouldn't I need the mass of the fork (m) to calculate the force exerted by gravity?
 Emeritus Sci Advisor HW Helper PF Gold P: 7,246 You will have "m" in two places in your equation. Use algebra to solve for m. I repeat:What is the net force being exerted upon the fork?
 P: 14 I can get up untill Fapp - m a(gravity) / a(applied) = m Now I am a bit confused on my next move. Is this right so far? Since m on the left is being multiplied by the acceleration of gravity I think I should divide to get rid of it. But once I do the right side would cancel out to zero.
 Emeritus Sci Advisor HW Helper PF Gold P: 7,246 Fapp - m g = m a 0.35 - m g = m (0.15) Not sure what you use for g: 10 m/s2 or 9.8 m/s2 or 9.81 m/s2 Put in the appropriate number for g & solve for m.
 P: 14 Yes, but as I said earlier I can get up until 0.35 - m g / 0.15 = m I can't successfully eliminate the LH m. I tried dividing and adding it to the RH
 Sci Advisor HW Helper PF Gold P: 5,920 Before you divide by 'a', your correct equation, per post 5 2nd line, was 0.35 - (m 9.8 m/s2) = m 0.15ms2 leaving off units, then 0.35 - (9.8m) = 0.15m Now this is algebra, add 9.8m to both sides 0.35 = 9.95m Now solve for m and convert to grams.
 P: 14 Thanks, that makes allot of sense.

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