Physics questions DUE IN 30 MIN

Physics 125 Test 3 Apr. 23, 2020 Name: Part 1: Below are 6 short work out questions. Answer any 5 of the 6 questions. YOU MUST SHOW ALL YOUR WORK TO RECEIVE ANY CREDIT. You may do the remaining question as a bonus. (You may use your book, notes, and old homework, BUT not other people.) 1. a) A mass travels around a loop. The surfaces are frictionless. Student A states that since the normal force is non-conservative, the energy of the mass at the bottom of the loop is not equal to the energy of the mass at the top of the loop. Student B states that the work done by the normal force would just be the normal force times the distance traveled by the mass going from the bottom of the loop to the top of the loop. Student C states that the energy at the bottom of the loop is equal to the energy at the top of the loop. Which student is correct? Explain your reasoning.

b) A bullet of mass m and velocity 𝑣" is fired into a block M initially at rest. The bullet remains in the block. Student A claims that the kinetic energy of the bullet-block system after the bullet strikes the block is equal to the kinetic energy of bullet before the bullet strikes the block. Student B disagrees. Which student is correct? Explain your reasoning.

c) A conservative force moves an object along three possible paths (A, B, and C). The object is moved from its initial position, i, to its final position, f. Student 1 claims that the ranking of the work done by this force along each of these paths is 𝑊$ > 𝑊% > 𝑊&. Student 2 claims that the work along the various paths are ranked 𝑊$ < 𝑊% < 𝑊&. Student 3 claims that 𝑊$ = 𝑊% = 𝑊&. Which student is correct? Explain your reasoning.

d) A 2 kg mass of putty traveling at 5 m/s collides and sticks to a 3 kg mass of putty traveling at 4 m/s as shown below. Student A claims that the V is given by 2(5) + 3(4) = (2+3)V. Student B states you need to use 𝐸(= 𝐸). Student C states neither A nor B are correct. Which student is correct? Explain your reasoning.

4. A 3 kg mass initially at rest is moving in 1-d. The potential energy of the 3 kg happens to be given by U = 8 - 4 𝑥 + 2 𝑥8. a) If the 3 kg mass is initially at x = 2 m, what is the energy of the 3 kg mass? b) What is the object’s velocity at x = 1m? c) At what values of x, will the 3 kg mass experience no force? E = v at x=1m = F = 0 when x = ______ and _________

4. A 10 kg mass initially traveling to the right at 15 m/s breaks up into 6 kg and 4 kg masses. The 4 kg mass has a velocity of 10 m/s and makes a 30" with the x-axis. What are the x and y components of velocity of the 6 kg mass?

Part 2: Below are 3 longer work out questions. YOU MUST SHOW ALL YOUR WORK TO RECEIVE ANY CREDIT. Answer all 3 questions. 1. Mass m, initially at rest, is compressing a spring of spring constant k by a distance x. The spring is released, and the mass travels around the circular loop of radius R.

a) Find an expression for the velocity of the mass at the top of the loop. 𝑣CDE = b) Find an expression for the normal force that the track exerts on the mass at the top of the loop. N =

c) After the mass travels around the loop, it starts traveling up an inclined plane. Find an expression for the maximum height, H, that the block reaches as it travels up the inclined plane? H =

2. Mass M, initially at rest, hangs from a string of length R. It is struck by a mass m traveling to the right with a velocity 𝑣". After the collision, the velocity of mass m is 𝑣"/3.

a) What is the velocity of M immediately after the collision? V = b) What is the velocity of mass M when it reaches the top of the circle?

𝑣CDE =

c) Find an expression for the tension in the string at the top of the circle. T = d) Find an expression for 𝑣" if M JUST makes it around the circle. 𝑣"=