L3 Differentiation
Question Bank

A hot-air balloon lifts off from a field. Its height above the ground, in metres, $t$ seconds after lift-off is modelled by
$ h = 12\sqrt{t + 25} - 60 $
for $0 \le t \le 300$.
Find the vertical velocity of the balloon 39 seconds after lift-off.
You must use calculus and show any derivatives that you need to find when solving this problem.
A sprinter's distance from the start line, in metres, $t$ seconds after the starting gun is modelled by
$ s = 10(t - 1 + e^{-t}) $
for $0 \le t \le 10$.
Find the sprinter's acceleration 1.5 seconds after the gun. Give your answer correct to 3 significant figures.
You must use calculus and show any derivatives that you need to find when solving this problem.
A ball is thrown straight up from a balcony. Allowing for air resistance, its height above the point of release, in metres, $t$ seconds after it is thrown is modelled by
$ h = 80(1 - e^{-0.5t}) - 20t $
for $0 \le t \le 3$.
Find the greatest height the ball reaches above the point of release. Give your answer correct to 3 significant figures.
You must use calculus and show any derivatives that you need to find when solving this problem.
You may assume that your answer is a maximum.

A lift in an apartment building starts from rest at the ground floor. Its upward velocity, in m/s, $t$ seconds after it starts is modelled by
$ v = 1.5te^{-0.5t} $
for $0 \le t \le 15$.
Find the time when the acceleration of the lift is zero.
You must use calculus and show any derivatives that you need to find when solving this problem.
A particle moves along a straight line. Its displacement from a fixed point $O$, in centimetres, $t$ seconds after it starts moving is
$ s = t^2 - 10t + 16\ln(t + 1) $
for $0 \le t \le 6$.
Find the times when the particle changes direction, and its displacement from $O$ at each of those times. Give the displacements correct to 3 significant figures.
You must use calculus and show any derivatives that you need to find when solving this problem.

After a large wave passes, a navigation buoy in a harbour bobs up and down. Its height above its rest position, in metres, $t$ seconds later is modelled by
$ y = 0.6e^{-0.2t}\sin 2t $
for $t \ge 0$.
Find the first time after $t = 0$ that the buoy is momentarily at rest, and its height above its rest position at that moment. Give your answers correct to 3 significant figures.
You must use calculus and show any derivatives that you need to find when solving this problem.