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