# Solving Physics Problems: Finding Speed and Displacement

• dronegun
In summary, The police officer calculates the speed of a Rover involved in a collision with a BMW using the coefficient of kinetic friction and the distance the cars skidded. Additionally, a rifle bullet traveling at 235 m/s causes a pendulum to swing upward in an arc, and the horizontal component of the pendulum's displacement is determined. Lastly, a 0.200 kg croquet ball collides with a stationary ball, with the second ball gaining half the original speed and a fraction of the original kinetic energy being transferred. Two principles, conservation of momentum and energy, are utilized to solve these problems.
dronegun
i am finding these hard. Any help appreciated

A 1.0 103 kg Rover collides into the rear end of a 2.2 103 kg BMW stopped at a red light. The bumpers lock, the brakes are locked, and the two cars skid forward 2.1 m before stopping. The police officer, knowing that the coefficient of kinetic friction between tires and road is 0.36, calculates the speed of the Rover at impact. What was that speed?

A 16 g rifle bullet traveling 235 m/s buries itself in a 3.1 kg pendulum hanging on a 2.8 m long string, which makes the pendulum swing upward in an arc. Determine the horizontal component of the pendulum's displacement.

A 0.200 kg croquet ball makes an elastic head-on collision with a second ball initially at rest. The second ball moves off with half the original speed of the first ball.
(a) What is the mass of the second ball?
kg
(b) What fraction of the original kinetic energy (KE/KE) gets transferred to the second ball?

You need to use two principles, conservation of momentum, and conservation of energy.

Remember momentum is conserved when the impact occurs, but energy is not.

For the first question, call the velocity before the impact V1 and after the impact V2. So you need two equations to find two unknowns. First equation: After the impact, the kinetic energy of the cars = the work done by friction of the tires. Second equation: During the impact, momentum is concerved.

I understand that solving physics problems can be challenging, but with practice and understanding of the concepts, it can become easier. Speed and displacement are fundamental concepts in physics and can be solved using the equations of motion and conservation of energy.

In the first problem, we can use the equation v^2 = u^2 + 2as to find the speed of the Rover at impact. Here, v is the final velocity (0 m/s since both cars come to a stop), u is the initial velocity (which we need to find), a is the acceleration (which we can find using the coefficient of kinetic friction and the weight of the cars), and s is the displacement (2.1 m). By plugging in the given values, we can solve for u and find the speed of the Rover at impact.

In the second problem, we can use the principle of conservation of momentum to find the horizontal component of the pendulum's displacement. We know that the momentum of the bullet before and after the collision should be equal, and we can use this to find the velocity of the pendulum after the collision. From there, we can use the equation s = ut + 1/2 at^2 to find the horizontal displacement of the pendulum.

In the third problem, we can use the principle of conservation of kinetic energy to find the mass of the second ball and the fraction of kinetic energy transferred. We know that the total kinetic energy before and after the collision should be equal, and we can use this to find the mass of the second ball. From there, we can use the equation KE = 1/2 mv^2 to find the fraction of kinetic energy transferred to the second ball.

I hope this helps in understanding how to approach and solve these types of problems. Remember to always pay attention to the given information, use the relevant equations, and check your units and calculations. With practice and perseverance, you can master solving physics problems.

## 1. How do I calculate speed using physics equations?

To calculate speed, you will need to use the equation speed = distance / time. This means that you will need to measure the distance traveled and the time it took to travel that distance. Then, divide the distance by the time to get the speed in units of distance over time, such as meters per second (m/s) or kilometers per hour (km/h).

## 2. What is displacement in physics?

In physics, displacement refers to the overall change in an object's position. It is measured in units of distance, such as meters or kilometers. Displacement takes into account both the distance an object has traveled and the direction in which it has moved, resulting in a single value that represents the object's overall change in position.

## 3. How do I find the displacement of an object?

To find the displacement of an object, you will need to know its initial position and its final position. Then, you can use the equation displacement = final position - initial position. This will give you a value representing the overall change in position of the object. Make sure to use the same units for both positions to ensure accuracy.

## 4. Can I use the same equation to find speed and displacement in any situation?

The equations for speed and displacement (speed = distance / time and displacement = final position - initial position) can be used in most situations where an object is moving at a constant speed. However, if the object is accelerating or decelerating, more complex equations will need to be used to accurately calculate speed and displacement.

## 5. How can I check the accuracy of my calculations for speed and displacement?

To check the accuracy of your calculations, you can use the equation velocity = displacement / time. If your initial and final positions are the same, then velocity should equal speed. Additionally, you can double check your units to make sure they are correct and use multiple measurements to ensure consistency in your calculations.

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