Is it possible for the momentum of an object to be mc. If not. why not? If so, under what condition?

A spaceship travels at $\mathbf{0}.\mathbf{8}\mathbf{c}$. As this spaceship covers $\mathbf{4000}\mathbf{km}$ from coast to coast, by how much will the time interval registered on an onboard clock differ from the time interval measured on ground?

According to Bob, on Earth, it is $\mathbf{20}\mathbf{ly}$ to Planet $\mathbf{Y}$. Anna has just passed Earth, moving at a constant speed $\upsilon$ in a spaceship, When Anna passes Planet $\mathbf{Y}$. She is $\mathbf{20}$ years older than when she passed Earth. Calculate $\nu$.

Can two moving objects of mass 2 and 3 stick together and form a single object of mass less than 5? Explain your-reasoning.

From a standstill. you begin jogging at $5m/s$ directly toward the galaxy Centaurus A. which is on the horizon $2\times {10}^{23}m$away.

(a) There is a clock in Centaurus A. According to you. How Will readings on this clock differ before and after you begin jogging? (Remember: You change frames.)

(b) The planet Neptune is between Earth and Centaurus $4.5\times {10}^{9}m$is from Earth- How much readings a clock there differ?

(c)What would the time differences if had instead begun jogging in the opposite direction?

(d) What these results tell you about the observations of a traveling twin who accelerates toward his Earth-bound twin? How would these observation depend on the distance the twins?

An electron accelerated from rest through a potential difference V acquires a speed of 0.9998c. Find the value of V.