Answer:
a) -210 ft/sec
b) -258 ft/sec
Step-by-step explanation:
given
a) s(t) = - 16t² - 130t + 1450
at t1 = 1:
s(1) = - 16(1)² - 130(1) + 1450
s(1) = - 16 - 130 + 1450
s(1) = 1304
at t2 = 4:
s(2) = - 16(4)² - 130(4) + 1450
s(2) = - 16(16) - 520 + 1450
s(2) = - 256 - 520 + 1450
s(2) = 674
average velocity
Va= [(s(t2) - s(t1)] / (t2 - t1)
⇒ Va= (674-1304)/(4-1)
= -210 ft/sec
the negative sign shows that the ball is moving downward
b) now, instantaneous velocity is give by derivative s'(t) at t
s'(t) = - 32t - 130
t = 4
s'(4) = - 32(4) - 130
s'(4) = - 128 - 130
s'(4) = - 258
therefore instantaneous velocity at t=4 sec
= -258 ft/sec
