Time dilation

A certain particle has a lifetime of 1.00 × 1 0 7 s 1.00 \times 10^{-7} \text{ s} when measured at rest. How far does it go before decaying if its speed was 0.99 0.99 c c when it was created?

The speed of light is c = 3 × 1 0 8 m/s. c = 3 \times 10^8 \text{ m/s.}

30 m 60 m 210 m 3 m

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3 solutions

Tasmeem Reza
Dec 27, 2014

Time dilation defines, Δ t = Δ t 1 ( v 2 c 2 ) \Delta t' = \frac{\Delta t}{\sqrt{1-\left ( \frac{v^{2}}{c^{2}} \right )}} where Δ t \Delta t is the time of particle's reference frame and Δ t \Delta t' is the time of our reference frame. Switching Δ t = 1.00 × 1 0 7 \Delta t=1.00 \times 10^{-7} , we obtain

Δ t = 1.00 × 1 0 7 1 ( ( 0.99 c ) 2 c 2 ) \Delta t' = \frac{1.00 \times 10^{-7}}{\sqrt{1-\left ( \frac{(0.99c)^{2}}{c^{2}} \right )}} Δ t = 1.00 × 1 0 7 1 0.9 9 2 \Rightarrow \Delta t' = \frac{1.00 \times 10^{-7}}{\sqrt{1-0.99^{2}}} = 7.0881 × 1 0 7 \quad \quad \quad \quad = 7.0881 \times 10^{-7}

So according to our reference frame the particle has traveled a distance s = 0.99 c × Δ t = ( 0.99 × 3 × 1 0 8 ) m s 1 × ( 7.0881 × 1 0 7 ) s s = 0.99c \times \Delta t' = (0.99 \times 3 \times 10^{8})ms^{-1} \times (7.0881 \times 10^{-7})s = 210.51657 =\boxed{210.51657}

Jalees Mughal
Jul 23, 2014

From time dilation, t= (1 x 10^-7)/(1-0.99^2)^1/2......... t=7.0888 x 10^-7............ s=v x t.............. s= 0.99 x 3 x 10^8 x 7.08881 x 10^-7......... s=210............

Siva Prasad
May 16, 2015

whereas for the particle frame their life time is unchanged and .. the length of the path got contracted . Lorentz factor plays in both time dilation and length contraction.

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