Physics problems: dynamics

Part 1


Problem 1.

If an object weighs 30 N on Earth, how much would it weigh on the moon?



Problem 2.

A child throws a ball downward from a tall building. Note that the ball is thrown, not dropped and disregard air resistance. What is the acceleration of the ball immediately after it leaves the child's hand?



Problem 3.

You are driving along an empty straight road at a constant speed u. At some point you notice a tall wall at a distance D in front of you. Would it require a larger force to (a) continue moving straight and decelerate to a full stop before the wall, or (b) turn left or right to avoid the wall? (to make the calculation easier assume that the turn is done at a constant speed along a circular path).



Problem 4.

How fast should the earth spin in order for a 150 lb human not to be able to walk on the ground?



Problem 5.

In the film 2001: A Space Odyssey, a wheel like space station achieves artificial gravity by spinning around its axis. If the station had a size of 2 km, how fast should it be spinning for the people inside to feel the same gravitational acceleration as on earth?





Problem 6.

A boy of mass 40 kg wishes to play on pivoted seesaw with his dog of mass 15 kg. When the dog sits at 3 m from the pivot, where must the boy sit if the 6.5 me long board is to be balanced horizontally?



Problem 7.

The drawing shows three particles far away from any other objects and located on a straight line. The masses of these particles are: partice A = 400 kg, particle B = 500 kg, and particle C = 100 kg. Find the magnitude and direction of the net gravitational force acting on each of the three particles (the direction to the right is positive).



Problem 8.

As part a of the drawing shows, two blocks are connected by a rope that passes over a set of pulleys. The block 1 has a weight of 400 N, and the block 2 has a weight of 600 N. The rope and the pulleys are massless and there is no friction.

(a) What is the acceleration of the lighter block?

(b) Suppose that the heavier block is removed, and a downward force of 600 N is provided by someone pulling on the rope, as part b of the drawing shows. Find the acceleration of the remaining block.



Problem 9.

Part a of the drawing shows a block suspended from the pulley; the tension in the rope is 80 N. Part b shows the same block being pulled up at a constant velocity. What is the tension in the rope in part b ?





Problem 10.

A uniform, solid metal disk of mass 6.0 kg and diameter 2.0 cm hangs in a horizontal plane, supported at its center by a vertical metal wire.  You find that it requires a horizontal force of 4 N tangent to the rim of the disk to turn it by 5 degrees, thus twisting the wire.  You now remove this force and release the disk from rest.

(a) What is the torsion constant for the metal wire? 

(b) Write the equation of motion for twist angle of the disk.




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