questions in physics

Reporter: Raymond P. Baldelovar Section: BSPE 1AProfessor: Adoracion S. Kuhutan Date: November 23, 2015

Questions in PhysicsDisplacement and Average Velocity

Problem 1: A man walks 7 km in 2 hours and 2 km in 1 hour in the same direction. 

a) What is the man's displacement from point A to B?

b) What is the man’s displacement from point B to C?

c) What is the man’s displacement from point A to C?

d) What is the man's average velocity for the whole journey?

Solution:

a. Δx = xB – xA

= 7 km – 0 km = 7 km

b. Δx = xC – xB

= 9 km – 7 km = 2 km

c. Δx = xC – xA

= 9 km – 0 km = 9 km

d.

0 km 7 km 9 km

Problem 2: A man walks 7 km East in 2 hours and then 2.5 km West in 1 hour. 

a) What is the man's displacement from point A to B?

b) What is the man’s displacement from point C to D?

c) What is the man’s average velocity for the whole journey?

Solution:

a. Δx = xB – xA

= 7 km – 0 km = 7 km

b. Δx = xC – xD

= 7 km – 4.5 km = 2.5 km

c.

0 km 7 km

4.5 km 7 km

Problem 3: You start walking from a point on a circular field of radius 0.5 km and 1 hour later you are at the same point.

a) What is your average velocity for the whole journey?

Solution:

a. If you walk around a circular field and come back to the same point where you started the displacement, which a change in position, is equal to zero. Since the displacement is equal to zero, the average velocity is also equal to zero.

Problem 4: John drove South 120 km at 60 km/h and then East 150 km at 50 km/h. Determine:

a) the displacement from point A to C?

b) the magnitude of the average velocity for the whole journey?

Solution:

a. The magnitude of the displacement is the distance AC between the final point and the starting point and is calculated using Pythagora's theorem as follows:

AC2 = 1202 + 1502 AC = √(14400+22500) = 30 √41 km

b.

Problem 5: A car travels 22 km south, 12 km west, and 14 km north in half an hour.

a) What is the final displacement of the car?

b) What is the average velocity of the car?

Solution:

a. The displacement is the distance between the starting point and the final point and is the hypotenuse DA of the right triangle DAE and is calculated using Pythagora's theorem as follows 

AE = 22 - 14 = 8 km 

DA2 = AE2 + ED2 = 82 + 122 = 64 + 144 = 208 DA = √208 = 4√13 km

b.

References:

How to Calculate Average Velocity. (n.d.). Retrieved November 20, 2015, from http://www.wikihow.com/Calculate-Average-Velocity

Solved Physics Problem: Average Velocity and Displacement. (n.d.). Retrieved November 20, 2015, from http://www.frigginphysics.com/2010/12/solved-physics-problem-average-velocity-and-displacement/

Velocity and Speed: Solutions to Problems. (n.d.). Retrieved November 20, 2015, from http://www.problemsphysics.com/mechanics/motion/velo_spe_solutions.html