Solve Perplexing Physics Problems with These Helpful Tips and Examples"

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In summary, the conversation discusses two physics problems involving velocity and acceleration. The first problem involves finding the time at which a second rock should be dropped from rest in order to arrive at the bottom of a cliff at the same time as a rock thrown with a velocity of 15 m/s. The second problem involves finding the average acceleration of a superball that bounces off a brick wall with a recorded contact time of 3.5 ms. Overall, the key to solving these problems is understanding the equations for velocity and acceleration and how to apply them in different scenarios.
  • #1
I'm having problems with some Physics problems; among them:

9. At the top of a cliff a 100 m high, a rock is thrown upward with velocity 15 m/s. How much later should a second rock be dropped from rest so both stones arrive simultaneously at the bottom of the cliff?

a. 5.05 s

b. 3.76 s

c. 2.67 s

d. 1.78 s

2. A 50-gram superball traveling at 25 m/s is bounced off a brick wall and rebounds at 22 m/s. A high-speed camera records this event. If the ball is in contact with the wall for 3.5 ms, what is the average acceleration of the ball during this time interval?

a. 13,428 m/s2

b. 6,715 m/s2

c. 857 m/s2

d. 20 m/s2

For 9), I thought I'd use v = u + at and find 2t after solving:
0 = 15 - 9.8t for t, and that would give me the answer... but I'm wrong.
Anyone know how I can go about this one?
And for 2), I really don't know what to do...

Thanks for any help.
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  • #2
For the first one, your answer was wrong because the first rock will have a downward speed of 15 m/s when it passes you again, and the other rock is dropped from rest. You need to drop the second rock before this point, and the only way to figure out when is to find the total time it will take each rock to hit the ground.

For the second, acceleration is the change in velocity over time. This problem is easier then it seems.
  • #3

I would suggest approaching these problems by first identifying the known variables and then using relevant equations to solve for the unknowns. For problem 9), the known variables are the initial velocity (15 m/s), the acceleration due to gravity (9.8 m/s^2), and the height (100 m). The unknown variable is the time (t) it takes for the first rock to reach the bottom of the cliff. Using the equation v = u + at, we can solve for t by rearranging the equation to t = (v-u)/a. Plugging in the known values, we get t = (0-15)/(-9.8) = 1.53 s. Since we want both rocks to arrive at the bottom at the same time, the second rock should be dropped 1.53 seconds after the first rock is thrown, leading to a total time of 3.06 s. This is closest to option d) 1.78 s.

For problem 2), the known variables are the mass of the ball (50 g), the initial velocity (25 m/s), the final velocity (22 m/s), and the time in contact with the wall (3.5 ms). The unknown variable is the acceleration (a) of the ball during this time interval. Using the equation a = (v-u)/t, we can solve for a by plugging in the known values: a = (22-25)/(3.5/1000) = -857 m/s^2. This matches option c).

In general, when solving physics problems, it is important to carefully identify the known and unknown variables and use relevant equations to solve for the unknowns. It may also be helpful to draw diagrams or make tables to organize the information and make the problem more visually understandable. Additionally, double-checking the units and making sure they are consistent throughout the problem can help catch any errors. With practice and careful attention to detail, you can become more confident in solving perplexing physics problems.

1. What is the definition of a "perplexing physics problem"?

A "perplexing physics problem" refers to a difficult or complex question or situation that requires knowledge and understanding of physics principles to solve.

2. How does one approach solving a perplexing physics problem?

One approach to solving a perplexing physics problem is to break it down into smaller, more manageable parts and use known principles and equations to solve each part. Another approach is to think creatively and use analogies or real-world examples to gain a better understanding of the problem.

3. Can a perplexing physics problem have multiple solutions?

Yes, a perplexing physics problem can have multiple solutions. In some cases, there may be more than one way to solve the problem, or there may be different approaches that lead to different solutions. It is important to carefully consider and evaluate each solution to determine its validity.

4. How do I know if my solution to a perplexing physics problem is correct?

The best way to determine if your solution to a perplexing physics problem is correct is to check your work and calculations. Make sure all units are consistent and that your answer makes sense in the context of the problem. If possible, it can also be helpful to ask for feedback from a peer or instructor.

5. Are there any tips or strategies for improving problem-solving skills in physics?

Yes, there are several tips and strategies that can help improve problem-solving skills in physics. These include practicing regularly, seeking help from instructors or tutors, breaking problems down into smaller parts, and using visual aids or diagrams to better understand the problem. It is also important to have a strong foundation in basic physics principles and equations.

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