Question

It has been said that in his youth George Washington threw a silver dollar across a river. Assuming that the wide, (a) what minimum initial speed river was 75 m was necessary to get the coin across the river and b) how long was the coin in flight?

Answer 1

Answer:

(a) 27.1 m/s

(b) 3.9 second

Explanation:

Let the speed is u.

Maximum horizontal range, R = 75 m

The range is maximum when the angle of projection is 45°.

(a) Use the formula for the maximum horizontal range

$R=\frac{u^{2}}{g}$

$75=\frac{u^{2}}{9.8}$

u = 27.1 m/s

(b) Let the time of flight is T.

Use the formula for the time of flight

$T=\frac{2uSin\theta}{g}$

$T=\frac{2\times 27.1 \times Sin45}{9.8}$

T = 3.9 second