Question

A l kg mass falls from a height of 10 m into a sand box. What is the speed of the mass just before hitting the sand box?
If it travels a distance of 2 cm into the sand before coming to rest, what is the average retarding force?
[1]
(a) 12 ms and 3600 N
(b) 14 ms- and 4900 N.
(c) 16 ms and 6400 N.
(d) 18 ms' and 8100 N​

Answer 1

Answer:

Answer is b

Velocity = √2gh

Velocity = 14m/s

By Work Energy Theoram

work done By all forces = ∆KE

-F × s = Kf - Ki

Kf = 0

ki = 1/2 m v^2 (m=1, v = 14m/s )

s = 2 × 10^-2m

F = 4900N

g = 10m/s2

Answer 2

When the mass hits the sand box,

• initial velocity = 0 m s^(-1) $\quad$

• acceleration = g = 10 m s^(-2)

• displacement = height = 10 m

Then, by third kinematic equation,

v² = u² + 2as

v² = 0² + 2 × 10 × 10

v² = 200 m^2 s^(-2)

v = 10√2 m s^(-1)

v = 14 m s^(-1)

Well, this is enough! We can conclude with the option (b) as the answer!