# Solving Mass from 2 Forces & Force of Impacting Bullet

• omonoid
In summary: So you would not void the negative sign. In summary, the first conversation discusses the calculation of mass based on two forces with different magnitudes and directions resulting in a specific acceleration. The second conversation involves finding the force exerted by a large fixed block of wood on a bullet based on its mass, initial and final velocities, and distance traveled.
omonoid
Part 1

1. The only two forces acting on a body have magnitudes of 20 N and 42 N and directions that differ by 60°. The resulting acceleration has a magnitude of 20 m/s2. What is the mass of the body?2. F=ma3. I am not sure how to solve this because I'm used to being able to use trig like cos and tan, but this problem doesn't create a triangle with 90 degrees

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Part 2

1. A bullet of mass 6.5*10-3 kg moving at 1150 m/s impacts with a large fixed block of wood and travels 8 cm before coming to rest. Assuming that the deceleration of the bullet is constant, find the force exerted by the wood on the bullet. 2. F=ma
V^2=Vi^2+2ax
3. V=0 Vi=1150 m/s x=.08 m solve for a and i got -8265625 m/s^2 then multiply by mass (6.5E-3) and get -53726.5625. Is this right? would i void the negative on a force?

Last edited:
Hi omonoid,

omonoid said:
Part 1

1. The only two forces acting on a body have magnitudes of 20 N and 42 N and directions that differ by 60°. The resulting acceleration has a magnitude of 20 m/s2. What is the mass of the body?

2. F=ma

Let me be picky here and say you should write this as Fnet=ma, that is, the sum of the forces equals m*a. Does that help? Have you added vectors together that were not perpendicular to each other?

3. I am not sure how to solve this because I'm used to being able to use trig like cos and tan, but this problem doesn't create a triangle with 90 degrees

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Part 2

1. A bullet of mass 6.5*10-3 kg moving at 1150 m/s impacts with a large fixed block of wood and travels 8 cm before coming to rest. Assuming that the deceleration of the bullet is constant, find the force exerted by the wood on the bullet.

2. F=ma
V^2=Vi^2+2ax

3. V=0 Vi=1150 m/s x=.08 m solve for a and i got -8265625 m/s^2 then multiply by mass (6.5E-3) and get -53726.5625. Is this right? would i void the negative on a force?

That number looks right to me. The minus sign is showing that the force is in the opposite direction of the initial velocity.

## 1. How do you calculate the mass from two forces?

To calculate the mass from two forces, you can use the formula: mass = force / acceleration. This formula is derived from Newton's second law of motion, which states that force is equal to mass multiplied by acceleration. So, by rearranging the formula, you can solve for mass by dividing the force by the acceleration.

## 2. What is the formula for calculating the force of an impacting bullet?

The formula for calculating the force of an impacting bullet is force = mass x acceleration. This is the same formula used to calculate the mass from two forces, but in this case, we are solving for force. The mass of the bullet and the acceleration at which it impacts the target are the key factors in determining the force of impact.

## 3. Can mass be calculated without knowing the force?

Yes, mass can be calculated without knowing the force. As mentioned earlier, you can use the formula mass = force / acceleration to calculate the mass from two forces. However, if you only know one force and the acceleration, you can rearrange the formula to solve for mass. Keep in mind that this will only give you the mass in relation to that single force and acceleration.

## 4. Why is it important to calculate the force of an impacting bullet?

Calculating the force of an impacting bullet is important for several reasons. It allows us to understand the potential damage and impact of the bullet on the target. This information can be used to design and test bulletproof materials and protective gear. Additionally, knowing the force of impact can help with forensic investigations and understanding the trajectory of the bullet.

## 5. Are there any other factors that can affect the calculation of mass from two forces?

Yes, there are other factors that can affect the calculation of mass from two forces. These include the direction and angle of the forces, as well as any external factors such as friction or air resistance. It is important to consider all of these factors when calculating mass to get an accurate result.

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