## PHY 3 questions

Physics 2201

Homework 2 Due 01/29/19. 10 points each

1. The three graphs below (two are velocity-time, one is position-time) describe one dimensional motions.

v

t

v

t

x

t

A

B

C

a. Use one or more of the following terms to describe the motion depicted on each graph:

“constant velocity”, “constant acceleration”, and/or “variable acceleration”. In each case briefly explain why the term applies.

b. Assume graph A represents the motion of an object tracked by a motion detector.

c. Sketch graph A on your solution sheet and label the graph to show where the object is slowing down, speeding up, moving towards the detector, moving away from the detector, respectively.

2. Consider the velocity-time graph below which describes the horizontal motion of an object and is referenced to the coordinate system also shown.

v

t

x = 0

object

a. At t=0 is the object moving left to right or right to left? How can you tell?

b. Is the object accelerating? If so in which direction, left to right or right to left, is the acceleration directed? Explain your reasoning.

c. Does the object continuously speed up, slow down, or do a little of both during the time interval displayed on the graph. Explain your answer and be specific.

d. Assume that at t=0 the object is crossing the origin (x=0). Sketch a position-time graph (x-t) consistent with the velocity-time graph.

 3. The figure at the right represents the position vs. clock reading of the motion of two balls, A and B, moving on parallel tracks. Carefully sketch the figure on your homework paper and answer the following questions:

a. Mark with the symbol ta along the t-axis any instant or instants at which one ball is passing the other. Explain your reasoning.

b. Which ball is moving faster at clock reading tb?

c. Mark with the symbol tc along the t-axis any instant or instants at which the balls have the same velocity. Explain your reasoning.

d. Over the period of time show in the diagram, which of the following is true for ball B?

1. It is speeding up all the time.

2. It is slowing down all the time.

3. It is speeding up part of the way and slowing down part of the way.

Again explain your reasoning for your choice and be specific.

## Physics homework

PHY 2201 Inclass –1/2219

1.A car drives north. At t-0, it passes a road sign. The distance north of the sign is given by

a. Find the expression for the car’s instantaneous velocity as a function of time.

b. Find the expression for the car’s acceleration as function of time. Does the car experience constant acceleration?

c. Find the average velocity between t=1s and t=3s.

d. What is the car’s instantaneous velocity at t=1s?

e. What is the cars instantaneous velocity and acceleration at t=3s?

2. A motor cyclist has constant acceleration of 4 m/s2. At t=0, he is 5m east of a road sign and is traveling east at 15 m/s.

a. We want to find his position a t=2.0 s. First, choose an origin for your coordinate system, and identify the initial and final states. Also write down the initial and final quantities.

b. Choose a constant acceleration equation which includes your desired quantity as the only unknown (if possible). In this case the unknown is the position at t=2s, solve for this position.

c. Follow the same procedures to find the velocity at t = 2 s.

d. Follow the same procedures to find the position when the motorcycle has a velocity of 25 m/s

3. A car traveling at 15 m/s passes a police car. At that instant, the police car accelerates at a constant rate of 3 m/s2 in pursuit. We wish to find how much time elapses before the officer catches the car.

a. Choose a coordinate system for this problem and identify the initial states starting when the car passes the police.

b. Define the final state or conditions which enables you to answer the above question.

c. To solve this problem identify the two equations (one for each vehicle) which satisfy part b. Solve for the unknown time.

4. A ball is thrown straight up in the air leaving your hand 1 m from the ground, with an initial velocity of 8 m/s.

a. Choose a coordinate system for this problem.

b. Is this a constant acceleration problem.

c. Find the time it takes to reach the maximum height.

d. Find the maximum height obtained by the ball.

e. Find the time to reach the ground.

f. Find the velocity when the ball hits the ground.

5. A ball is thrown at 25 m/s at an angle of 250 above the horizontal.

a. Choose a coordinate system and sketch the motion of the ball.

b. Find the initial velocity of the ball in the x and y directions.

c. Find when the ball reaches its highest point.

d. Find how long it takes to return to the ground.

e. How far did the ball go the x direction.

y

t

t

=

+

2

5

1