Think Like a Physicist 5

1.  Why can't you open a door by pushing on its hinge side?

2.  You can do push-ups with either your toes or your knees acting as the pivot about which your body rotates.  When you pivot about your knees, your feet actually help you lift your head and chest.  Explain.

3.  When you begin to walk forward, what exerts the force that allows you to accelerate?

4.  A toy top spins for a long time on its sharp point.  Why does it take so long for the friction to slow the top's rotation?

Torque Problem (invisible fulcrum)

Two construction workers carry a 500 N load using a pole 2.55 m long and weighing 20 N. The load is placed at the middle of the pole. One worker supports the pole at one end. Where should the heavier worker support the pole if he is to shoulder part of the load in the ratio 3:2 with the other worker?

Think Like a Physicist 4

Explain why the Coke Zero can balance as shown in the figure.

Think Like a Physicist 3

You cannot throw an egg against a brick wall without breaking the egg, but you can throw it with the same velocity into a sagging sheet without breaking the egg.  Explain.

Momentum Conservation: Inelastic Collision

A 5.00-g bullet is fired with a velocity of 100 m/s toward a 10.0-kg stationary solid block resting on a frictionless surface.

a.  What is the change in momentum of the bullet if it is embedded in the block?

b.  What is the change in momentum of the bullet if it ricochets in the opposite direction with a speed of 99 

      m/s- almost the same speed as it had originally?

Please click on the link to see a bigger view: http://www.youtube.com/watch?v=JyLWG5JlFbo

A 50-kg girl throws a 5.0-kg pumpkin of 10 m/s to a 50-kg boy, who catches it.  If both are on a frictionless frozen lake, how fast does each of them move backward?

Please click on the link to see a bigger view: http://www.youtube.com/watch?v=Vf7o9zSy6JM

More Friction Problems

This is problem #10 p. 103 of your textbook.

*Note: THERE SHOULD BE A SQUARE ON 5.3 m/s.

Click on the link to see a bigger view: http://www.youtube.com/watch?v=zSwb-4i2jMs

This is problem #4 in p. 102 of your textbook.

Click on the link to see a bigger view: http://www.youtube.com/watch?v=6HaSs1KeqVk

Friction Problems

1.  A man is dragging a tank up the loading ramp of a mover's truck.  The ramp has a slope angle of 20.0^o, and the man pulls upward with a force F whose direction makes an angle of 30.0^o with the ramp.

a.  How large a force F is necessary to in order for the component F_x parallel to the plane be 28.0N?

b.  How large will the component F_y be?
c.  What is the weight of the trunk?

Please click on the link to see a bigger video: http://www.youtube.com/watch?v=zPS896d0VjU

2.  A 200-N box is placed on top of an inclined plane whose angle of is 30.0^o from the horizontal.  Determine the force needed to keep it in its position.  neglect friction.

Please click on the link to see a bigger video: http://www.youtube.com/watch?v=XBp24y7Vc3I

Think Like a Physicist 2

Why must a sharp shooter or an archer aim somewhat above her target? Why can't she simply aim directly at the bull's eye to hit it?

Think Like a Physicist

Out in deep space, far from any celestial object that exerts significant gravity, would an astronaut weigh anything? Would that astronaut have a mass?  Explain.

Projectile Motion Sample Problems 4 to 7

Please pardon my projectile hair. 

4.  A book slides off a horizontal table top with a speed of 4 mps.  It is observed to strike the floor in 0.5 seconds.  Find

a.      the height of the table top above the floor.

b.      the horizontal distance from the edge of the table to the point where the book strikes the floor.

c.       the horizontal and vertical components of its velocity when it reaches the floor. 

Please click on the link to see a bigger view: 

http://www.youtube.com/watch?v=4h0V-4TonDc 

5. A marksman fires a .22-caliber rifle horizontally at a target; the bullet has a muzzle velocity of 900 fps.  How much does the bullet drop in flight if the target is
       a.      50 yards away?
       b.      150 yards away?

Please click on the link to see a bigger view:

http://www.youtube.com/watch?v=nYZzUpO9LB0

6.  A baseball is thrown at an angle of 53^o above the horizontal with an initial speed of 40 mps.

a.      What is the maximum height above the thrower’s hand reached by the baseball?

b.      How long does it take to reach the maximum height?

c.       At what two times is the baseball at a height of 25 m above the point from which it was thrown?

Please click on the link to see a bigger view:

http://www.youtube.com/watch?v=kV5eonkVM6E

7.  A man stands on the roof of a building that is 50 m tall and throws a rock with a velocity of 60 mps at an angle 37^o above the horizontal.  Calculate:
a.      the maximum height, above the roof, reached by the rock;
b.      the magnitude of the resultant velocity of the rock just before it strikes the ground;
c.       the horizontal distance from the base of the building to the point where the rock strikes the ground.

Please click on the link to see a bigger view:

http://www.youtube.com/watch?v=mCp6WMy2Bd8

Projectile Motion Sample Problems

A projectile is an object upon which the only force acting is gravity. - physicsclassroom.com

1.  A baseball rolls on top of a flat roof 25 m high at a speed of 25 m/s.
a. The ball reaches the edge of the roof.  How long would it take the ball to reach the ground?
b. Find the range of the baseball.

Click on the link to see a bigger view: http://www.youtube.com/watch?v=VMcqnZbATAw

2. A basketball was thrown at a speed of 35 m/s and projected at an angle of 35⁰.
a.  How long will the basketball be in the air.
b.    Find the range of the basketball.

Click on the link to see a bigger view: http://www.youtube.com/watch?v=WdmbDiBudAc

3.  A motorcycle stunt rider rides off the edge of a cliff with a horizontal velocity of magnitude 5 mps.  Find the rider’s position and velocity after ¼ seconds.

Click on the link to see a bigger view: http://www.youtube.com/watch?v=C1UoytrdB7Q