a. 2.8 m/s
suppose that at the height of 0 m, the path of the pendulum is lowest.
if we use law of conservation of energy, the pendulum will have zero kinetic energy or k.e when it is at highest point, because k.e happens during movement of object and at the highest point all the energy will be p.e
similarly, when the pendulum reaches at the lowest point, the height becomes zero and the p.e also becomes zero. now all the energy will be k.e
k.e= 1/2 m v^2
in question, we are asked about the speed as the pendulum it reaches the lowest point of its path. like we mentioned p.e will be zero at lowest point because of zero height. and also we will use law of conservation of energy because no energy has been lost from system.
1/2 m v^2 = mgh
taking sq.root at both sides
v= under root 2 gh
v=under root 2x 9.8 m/s x0.4 m
v=under root 7.84
hope it !
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