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A 15 g bullet is fired horizontally into 3 kg block of wood 10 cm above the intial level,the velocity of bullet is..

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11 Years agoGrade Select Grade
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Profile image of Askiitians Tutor Team
ApprovedApproved Tutor Answer1 Year ago

To determine the velocity of the bullet when it is fired horizontally into a block of wood, we can use the principles of conservation of momentum and the equations of motion. Let's break this down step by step.

Understanding the Scenario

We have a bullet with a mass of 15 grams (which is 0.015 kg) that is fired horizontally into a wooden block with a mass of 3 kg. The bullet strikes the block at a height of 10 cm above its initial level. Our goal is to find the velocity of the bullet just before it hits the block.

Key Concepts Involved

  • Conservation of Momentum: In a closed system, the total momentum before an event must equal the total momentum after the event.
  • Projectile Motion: The bullet will follow a parabolic path after being fired, influenced by gravity.

Calculating the Time of Flight

First, we need to determine how long it takes for the bullet to fall 10 cm (0.1 m) vertically. We can use the equation of motion for free fall:

h = 0.5 * g * t²

Where:

  • h = height (0.1 m)
  • g = acceleration due to gravity (approximately 9.81 m/s²)
  • t = time in seconds

Rearranging the equation to solve for time (t):

t = √(2h/g)

Substituting the values:

t = √(2 * 0.1 m / 9.81 m/s²) ≈ √(0.0204) ≈ 0.143 s

Finding the Horizontal Distance

Next, we need to find the horizontal distance traveled by the bullet during this time. If we denote the horizontal velocity of the bullet as v, the horizontal distance d can be expressed as:

d = v * t

Applying Conservation of Momentum

When the bullet embeds itself into the block, we can apply the conservation of momentum. Before the collision, the momentum of the bullet is:

p_initial = m_bullet * v

After the collision, the combined mass of the bullet and block moves together with a common velocity V:

p_final = (m_bullet + m_block) * V

Setting the initial momentum equal to the final momentum gives us:

m_bullet * v = (m_bullet + m_block) * V

Calculating the Final Velocity

To find the velocity of the bullet, we need to express V in terms of the known quantities. However, we need more information about the final velocity after the collision, which typically requires additional data such as the distance traveled horizontally or the final velocity of the block. If we assume that the bullet comes to a stop after hitting the block, we can simplify our calculations.

For example, if we assume the bullet transfers all its momentum to the block, we can express the final velocity as:

V = (m_bullet * v) / (m_bullet + m_block)

Conclusion

In summary, to find the bullet's velocity, we need to know either the distance it traveled horizontally or the final velocity of the block after the collision. If you have that information, we can plug it into our equations to find the bullet's initial velocity. If not, we can only express the relationship between the bullet's velocity and the final velocity of the block.

Profile image of Askiitians Tutor Team
ApprovedApproved Tutor Answer1 Year ago

To determine the velocity of the bullet when it is fired horizontally into a block of wood, we can use the principles of conservation of momentum and the equations of motion. Let's break this down step by step.

Understanding the Scenario

In this problem, we have a bullet with a mass of 15 grams (which is 0.015 kg) that is fired into a wooden block with a mass of 3 kg. The bullet strikes the block horizontally and embeds itself in it. The block is initially at rest, and we want to find the bullet's velocity just before impact.

Key Concepts

  • Conservation of Momentum: The total momentum before the collision is equal to the total momentum after the collision, assuming no external forces act on the system.
  • Kinematics: We can use the equations of motion to analyze the vertical drop of the block after the bullet embeds itself.

Applying Conservation of Momentum

Before the collision, the momentum of the system is solely due to the bullet since the block is at rest. After the bullet embeds itself in the block, we can express the momentum of the combined system.

The momentum before the collision can be expressed as:

p_initial = m_bullet * v_bullet

After the collision, the momentum is:

p_final = (m_bullet + m_block) * v_final

Setting these equal gives us:

m_bullet * v_bullet = (m_bullet + m_block) * v_final

Vertical Motion of the Block

When the bullet embeds itself in the block, the block will start to fall due to gravity. The vertical distance it falls is 10 cm (0.1 m). We can use the kinematic equation for free fall to find the time it takes for the block to fall this distance:

h = 0.5 * g * t^2

Where:

  • h: vertical distance (0.1 m)
  • g: acceleration due to gravity (approximately 9.81 m/s²)
  • t: time in seconds

Rearranging the equation gives us:

t^2 = (2 * h) / g

Substituting the values:

t^2 = (2 * 0.1) / 9.81

t^2 = 0.0204

t ≈ 0.142 s

Finding the Final Velocity

The final velocity of the block and bullet system just after the collision can be calculated using the horizontal distance traveled during the time of fall. Since the bullet is fired horizontally, we can assume it travels a certain horizontal distance while the block falls.

Let’s denote the horizontal distance traveled by the bullet as d. The horizontal velocity of the bullet just before impact can be expressed as:

v_bullet = d / t

Combining the Equations

Now we can substitute this back into our momentum equation:

m_bullet * (d / t) = (m_bullet + m_block) * v_final

Since we want to find the bullet's velocity, we can rearrange this equation to solve for v_bullet:

v_bullet = (m_bullet + m_block) * v_final * t / m_bullet

To find v_final, we can use the fact that the block will have a certain velocity after the bullet embeds itself, which can be calculated from the vertical motion and the time of fall.

Final Calculation

To summarize, we need to know the horizontal distance d to find the bullet's velocity. If we assume a certain distance, we can plug that into our equations to find the bullet's velocity. For example, if the bullet travels 1 meter horizontally while the block falls, we can substitute that value into our equations to find:

v_bullet = d / t

Substituting d = 1 m and t ≈ 0.142 s gives:

v_bullet = 1 / 0.142 ≈ 7.04 m/s

Thus, the bullet's velocity just before impact would be approximately 7.04 m/s, given the assumptions made about the horizontal distance traveled. Adjusting the distance will yield different velocities, so it's essential to have that information for precise calculations.