Question

50. a kangaroo can jump over an object 2.50 m high. (a) calculate its vertical speed when it leaves the ground. (b) how long is it in the air?

Answer 1

Answer:

The easiest way to do this is to realize that the time to fall is the same as the rise time (conservation of energy can easily verify this)

S = 1/2 g t^2      time to fall 2.5 m

t = (5 / 9.8)^1.2 = .714 sec         time in air

v = a t = 9.8 * .714 = 7 m/s     initial vertical speed

Check:

S = v t - 1/2 g t^2       where v is the initial vertical speed

S = 7 * .714 - 4.9 * .714^2 = 2.5 m        total vertical distance traveled