How long does it take for a 1000kg object to fall 45m? (Ignore air resistance and assume constant acceleration from gravity of -10m/sec^{2})

A) 0.045 seconds

B) 3 seconds

C) 4.5 seconds

D) 9 seconds

**Explanation**

Mass does not affect time for a projectile to fall in constant gravitational acceleration. For a 45m fall, use the equation y = v_{0}t+1/2at^{2}, with y = 45m, v_{0 }= 0m/sec, and a = 10m/sec^{2}.

45m = 1/2*(10m/sec^{2})t^{2}, 9sec^{2 }= t^{2}, t = 3 seconds.

A) 0.045 seconds, incorrect, This answer divides the distance by the mass.

B) 3 seconds, correct.

C) 4.5 seconds, incorrect, This answer divides the distance by the gravitational acceleration.

D) 9 seconds, incorrect, This answer uses an incorrect formula proportional to t rather than t^{2}.