PHY-2048C – Fall 2020 SI with Camilo

Exam 1 Practice Test

Disclaimer: This practice test does not necessarily cover all the material that is going to appear on the test, the questions are not the same as the actual test, and should not be used as the sole study guide for the test.

1. Three forces act on a point: 3 N at 0°, 4 N at 90°, and 5 N at 217°. What is the net force?

magnitude direction x-component y-component

first force 3 N 0° +3 N 0 Nsecond force

4 N 90° 0 N +4 N

third force 5 N 217° −4 N −3 N

resultant 1.4 N 135° −1 N +1 N

2. A ball thrown up vertically returned to the thrower after 4s. What was the velocity with which the ball was thrown?

V f=V 0+a∗t

0=V 0+a∗t 1/2

V 0=−g∗t 1/2

V 0=¿ -(- 9.8)* (4/2)= 19.6 m/s

3. Which of the bellow can be true at the same time?

I. Velocity: Constant and Acceleration: ConstantII. Velocity: Constant and Acceleration: Changing

III. Velocity: Changing and Acceleration: ConstantIV. Velocity: Changing and Acceleration: Changing

Answer: E

4. A car begins driving from a stationary position. It accelerates at 4 m/s2 for 10 seconds, it then travels at a steady speed for another 10 seconds, all in the same direction. How much distance has it covered since it started driving?

A) A. 200 mB) B. 400 m C) C. 600 m D) D. 800 m

v f=v0+a∆ t=0+4∗10=40m /s

5. A motorist traveling at a constant 15m/s passes a school crossing where the speed limit is 10m/s. Just as the motorist passes the school-crossing sign, a police officer on a motorcycle stopped there starts in pursuit with constant acceleration of 3m/s^2.

a) How much time elapses before the officer passes the motorist?

b) At that time what is the officers speed?

c) At that time how far has each vehicle traveled?

6. A batter hits a baseball so that it leaves the bat at speed V 0 = 37m/s at and angle of 53.1 degrees.

a) Find the velocity (magnitude and direction) at t = 2 seconds

b) Find the time when the ball reaches its highest point and the height at this time

c) Find the horizontal distance that the ball travels as it hits the ground

7. A stone is thrown upward from the top of a building at an angle of 30° to the horizontal and with an initial speed of 20 m/s. The point of release is 45 m above the ground. How long does it take for the stone to hit the ground? What is the stone's speed when it hits the ground?

8. Starting from rest, a car first accelerates to 25m/s and the begins to break. 48 seconds after starting, it is moving at 14m/s. What is the average acceleration in this 48s interval?

aavg=∆V∆ t

=V f−V 0t f−t 0

=14−048−0

=0.29m /(s2)

9. A senior physics class conducting a research project on projectile motion constructs a device that can launch a cricket ball. The launching device is designed so that the ball can be launched at ground level with an initial velocity of 28 m s–1 at an angle of 30° to the horizontal.a) At what time will the ball reach its maximum height?b) What is the maximum height that is achieved by the ball?c) What is the acceleration of the ball at its maximum height?

Ans:

10. Bob is shot out of a cannon with a speed of 20 m/s at an angle 30 degrees above the horizontal. He is headed for a wall that is located 25 m away from the launching point. Calculate the height along the wall that Bob hits. Also calculate Bob's max height along the trajectory.

11. A ball is being swung by a rope in a uniform circular motion. The rope is 10 m long and the ball’s speed is a constant 20 m/s. Find the ball’s acceleration.

12. A traffic light weighting 122 N hangs from a cable tied to two other cables fastened to a support. The upper cables make angles of 37∘ And 53∘ with the horizontal. These upper cables are not as strong as the vertical cable, and will break if the tension in either one of them exceed 100N. Will the traffic light remain hanging or will one of the cables break? Draw free body diagram and calculate tensions in all cables.

13. A waitress shoves a ketchup bottle with mass 0.45 kg to her right along a smooth, level lunch counter. The bottle leaves her hand moving at 2.8m/s, then slows down as it slides because of a constant horizontal friction force exerted on it by the countertop. It slides for 1.0 m before coming to rest. What are the magnitude and direction of the friction force acting on the bottle?

14. Two forces act on a 3.3-kg mass that undergoes acceleration a ⃗ =0.86i−0.32j m/(s^2). If one force is −0.90i−2.1jN, what's the other?

F x 1=−0.90 i−2.1 j N

F xnet=max=F x 1+Fx 2

F x 2=max−Fx1=3.3∗0.86+0.9=3.7N

F ynet=ma y=F y1+F y 2

F y 2=may−F y 1=3.3∗(−0.32)+2.1=1.0 N

F2=(3.7 i+1.0 j)N