what is the initial velocity of an object thrown straight up that takes 5 seconds to reach its highest point?

50 [m/s].

Explanation:

1) formula is: V-V₀=g*t, where V₀ - final velocity (it is 0), V - required initial velocity, g≈10 [m/s²] and t - elapsed time.

2) according to the formula above:

V=g*t; ⇒ V=5*10=50 [m/s].

answer: 2×10^-2kg

explanation: density= mass per volume

vol=mass/density

converting to s.i units we have;

3÷1000kg = 0.003

1.5÷100m = 0.15

0.003/0.15 = 0.02kg