385

Physics Units Level: High School

Does a negative acceleration necessarily imply that a body is slowing down ? What (or who ) determines the sign if the acceleration in a particular problem ?



384

Physics Units Level: High School

By definition , 1 inch precisely equals 2.5400 centimeters . A length is measured to be 3.2 feet , and after conversion to centimeters this length is reported to be 97.54 centimeters . Explain what is wrong with this conclusion .



383

Physics Kinematics Level: High School

A punter kicks a punt 4.0 seconds later the punt return fields the punt 40 yards down field . Assume that he receives the ball at the same height that it was punted .Find ,

a. Vxo

b. Vyo

c. Vo




382

Physics Kinematics Level: High School

A ball is thrown from the ground vertically upward at 20 m/s .

(a) how high does it go up ?

(b) how long to reach its highest point

(c) how long till it hits the ground ?

(d) What is the velocity that it has when it returns to the level from which it started ?




381

Physics Kinematics Level: High School

A mountain climber throws a stone straight down into a mountain pool 50 meters below . The stone has an initial velocity of 2 m/s straight down .

(a)How long till the stone hits the water .

(b) Suppose he throws a second stone 1 second later . With what velocity would he have to throw the second stone if both stones hit at the same time .




380

Physics Kinematics Level: High School

A plane flies 40 km due north in level flight . The pilot then flies 100 km at a heading of 45 degrees east of north . Next he flies 20 km due south . Find the displacement vector that describes his final position .



379

Physics Kinematics Level: High School

A projectile is launched into the air with a velocity of 30 m/s at an angle of 30 from the horizontal . Assume that there is no friction and that the ground is level . Find Vxo and Vyo , the maximum height the projectile reaches , the distance it travels when it hits the ground , and the final velocity of the ball (magnitude and direction)



378

Physics Measurements Level: High School

Given a sheet of paper and a ruler , can you think of two indirect measurements you could make ? What direct measurements would you need in each case ?
Two indirect measurements are

(i) Perimeter 2 [l+b]

(ii) Area l x b

Direct measurements .

(i) length l

(ii) width b




377

Physics Units Level: High School

Significant figures

Alice measures the diameter of a CD and gets a value of 117 mm , so she reports the value of the circumference as 367.5663404700058 mm . What wrong with this picture ?
Since the direct measurement has three significant figures (d=117 mm) , the indirect measurement , that is the circumference is calculated from it . Thus it can’t have more than 3 significant figures in the answer .



376

Physics Work,Power & Energy Level: High School

The diagram shown at depicts two pucks on a frictionless table. Puck II four times as massive as puck I. starting from rest, the pucks are pushed across the table by two equal forces.

(a) Which puck will have the greater kinetic energy upon reaching the finish line ? Explain

(b) Which puck will reach the finish line first ? Explain.




375

Physics Kinematics Level: High School

A sky diver , with parachute unopened, falls 625 m in 15 seconds . Then she opens her parachute and falls another 356 m in 142 s . what is her average velocity(both magnitude and direction) or her entire fall ?



374

Physics Kinematics Level: High School

An 18 year old runner can complete a 10. km course with an average speed of 4.38 m/s . A 50 year old runner can cover the same distance with an average speed of 4.27 m/s . How much later should the younger runner start in order to finish the course at the same time as the older runner ?



373

Physics Kinematics Level: High School

Give an example for which the velocity of an object is zero for just an instant of time , but its acceleration is zero .
If we throw a ball up , when it reaches the highest point , its velocity becomes zero for just an instant of time , but its acceleration is not zero . It is still having an acceleration equal to acceleration due to gravity g’.



372

Physics Vectors Level: High School

Two buses depart from Chicago , one going to Newt York and one to San Francisco . Each bus travels at the speed of 30 m/s . Do they have equal velocities ? Explain .
No. they do not have the same velocity . The velocity is a vector and has magnitude as well as direction . So , the speed of the two buses traveling to New York and to San Francisco are the same but the direction are different . Thus velocities are not equal .



371

Physics Vectors Level: High School

The magnitude of the force vector F is 280 newtons . The x component of this vector is directed along the +x axis and has a magnitude of 150 newtons . The y component points along the +y axis

(a) Find the direction of F relative to the +x axis

(b) Find the component of F along the +y axis


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