# Basic Physics question?

Both of these questions please

### 2 Answers

- NCSLv 74 weeks agoFavourite answer
004/

thrown ball: y = 21*t - ½*9.8*t²

dropped ball: y = 39 - ½*9.8*t²

set y = y; gravity terms cancel

t = 39m / 21m/s = 1.9 s

005/

A 7.6 m tall window? Really?

Passing the window, Vavg = h / t = 7.6m / 0.214s = 35.5 m/s

But also Vavg = ½(u + v)

where u is the velocity at the top of the window

and v is the velocity at the bottom.

Furthermore, v = u + gt = u + 9.8m/s²*0.214s = 2.10 m/s

so Vavg = 35.5 m/s = ½(u + u + 2.10m/s) = u + 1.05m/s

u = 34.5 m/s

h = u² / 2g = (34.5m/s)² / 2*9.8m/s² = 61 m

bonus:

If you meant a window of height 1.6 m, then

Vavg = 7.48 m/s = u + 1.05m/s

u = 6.43 m/s

h = u² / 2g = (6.43m/s)² / 19.6m/s² = 2.1 m

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- Anonymous4 weeks ago
#5 was 61 m but #4 was not 1.9s, can you try again? Thanks