Negative; Zero. Cannot be determined from the given information. The change in k

Question

Negative; Zero. Cannot be determined from the given information. The change in kinetic energy of the box is: Positive; Negative; Zero. The change in potential energy of the box is: Positive; Negative; Zero. How many of the following are units of energy: Joule, horsepower, kilowatt-hour? None; One; Two; Three. If an object's kinetic energy must be doubles, while its mass is constant, the speed must be multiplied by: squareroot 2; 2; 4; none of the above. You are holding a 100-kg barbell over your head at a height of 2 m. The work you are doing equals: -19,600 J; Zero J; 19,600 J. A 400 kg roller coaster car starts from rest at the top of a 90 m drop. Neglect friction and air resistance (except for question 16). Questions 11-16 refer to this situation. The car's speed at the bottom of the ride is: Less than 20 m/s; Between 20 and 40 m/s; Greater than 40 m/s. If the car's mass were doubled its speed at the bottom of the ride would: Double; Quadruple; Halve; Remain the same.

Explanation / Answer

8. C   joule and kilowatt hour are the units of energy , horsepower is unit of power

9. A   kinetic energy k = 1.2 mv^2, k1/k2 = v1^2/v2^2

       k1/2k1 = v1^2/v2^2 ==> v2^2 = 2 v1^2 ==> v2 = sqrt(2)* v1 m/s

10. B work done is W = F*s cos theta here theta is 90 so cos 90 = 0,

   work done is zero

11. C conservation of energy GPE = K.E

  
       mgh = 1/2 mv^2 ==> v^2 = 2*gh ==> v = sqrt(2gh)

               v = sqrt(2*9.8*90)= 42 m/s

option C greater than 40 m/s

12. D if the car's mass were doubled its speed at the bottom of the ride will be same no significance of mass

   so option D is correct

       OR

under free fall mass is insignificant.

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