Question: The position of a particle is given by

r(t)=4ti^+2t2j^+5k^ where t is in seconds and r in metre. Find the magnitude and direction of velocity v(t), at t=1 s, with respect to x-axis

A) 42 ms1,45

B) 42 ms1,60

C) 32 ms1,30

D) 32 ms1,45

Answer: 42 ms1,45

Sol:

V=drdt=4i^+4j^+0k^  at t=1sec V=4i^+4(1)j^ |V|=42+42=42 tanα=44=1 α=45