Posted by tanya on .
A model airplane of mass 0.7 kg is attached
to a horizontal string and ﬂies in a horizontal
circle of radius 5.6 m, making 1.6 revolutions
every 7 s. (The weight of the plane is balanced
by the upward “lift” force of the air on the
wings of the plane.)
The accelaration due to the gravity is 9.81
m/s2.
Find the speed of the plane

physics 
drwls,
Forget about the weight data. You would need the lift coefficient and wing area to get the velocity from the weight.
The plane travels 1.6*2*pi*5.6 meters in 7 s.
That is all you need to compute the speed.