Question

Calculate the wavelength of α-particle moving with a speed of 2x106m/s.
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Answer 1

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this is what i did but i dont seem to get the right answer which apparently is supposed to be 7.3x10^-15 m

so i did:

1/2mv^2 = eV

1/2 x 6.4x10^-27 x v^2 = 4.0x10^6

v= 3.5x10^16 ms^-1

Wavelength = h/mv

=6.63x10^-34 / 6.4x10^-27 x 3.5x10^16

but i dont get the right answer, could someone please tell me where im going wrong. Thanks.