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In a hydrogen atom in its lowest energy state, the single electron and the single proton are separated by a tiny distance called the Bohr radius, 5.29×10−11 m. The proton carries a charge e = 1.60×10−19 C. (a) What is the strength of the electric field generated by the proton at the Bohr-radius distance? K = 8.9 x 109  N m 2/C2

A positively charged insulating rod is brought close to an object that is suspended by a string.If the object is repelled away from the rod we can conclude

A 1-kg block is lifted,at constant velocity, vertically 1m by a boy. The work done by the boy is about: (g = 9.8 m/s2)

The cutting cord on a gas-powered weed cutter is 0.16 m in length.  If the motor rotates at the rate of 20 rev/s, what is the approximate linear speed of the end of the cord?

A 7.6 kg chair is pushed across a frictionless floor with a force of 42 N that is applied at an angle of 22° downward from the horizontal. What is the magnitude of the normal force on  the chair?

A bullet with mass 12.0g  travels 415 m/s. Find its kinetic energy. ( Hint: Convert 12.0 g to kg )  

A car is negotiating a flat circular curve of radius 50 m with a speed of 20 m/s.  The maximum centripetal force (provided by static friction) is 1.2 × 104 N. What is the centripetal acceleration of the car?

True or False: Electric force is a contact force.

A 500-kg sack of coal is dropped on a 2000-kg railroad flatcar which was initially moving at 3m/s as shown. After the sack rests on the flatcar, the speed of the flatcar is:

A 200-N/C electric field is in the positive x direction. The force on an electron ( 1.60 x 10 -19 C)  in this field is: