30. A helicopter on a landing pad weighs 2000 newtons. As the helicopter blades begin to turn, they push air downward with increasing force. When will the helicopter lift off the ground?

a. When the force of the downward air is greater than the helicopter’s weight.
b. When the force of the downward air is exactly twice the helicopter’s weight.
c. When the force of the downward air is exactly half of the helicopter’s weight.
d. When the force of the downward air is exactly equal to the helicopter’s weight.

the first american roller coaster was the mauch chunk switchback railway, built in the mountains of pennsylvania in the mid-1800s. the track, originally built to send coal to a railway, was reconfigured as a "scenic tour."

i had this question and the answer was 3.15 miles.

martina travels from school to her mom's office. from there, she walks to school. after school, she walks to the library and then to a friends house before finally ending back at home. find martina's total distance traveled.

a) 0 miles  

b) 0.4 miles  

c) 1 mile  

d) 3.15 miles