Question

A, B, C or D?

A load of 4900 N is dropped through a vertical distance of 2.0m onto a stationary mass of 1500kg. The weight does not rebound.

What is the downward speed of the combined masses immediately after impact?

A: 1.6 m/s
B: 2.1 m/s
C: 9.8 m/s
D: 15 m/s

Answer 1

`~~1.6" ms"^-1`

Explanation:

The speed `v` the load acquires after dropping through a distance of 2 m is given by

`v^2 = u^2+2gx qquad implies qquad v^2 = 2times 9.8 times 2 " m"^2"s"^-2`

Thus `v = 6.26" ms"^-1`
Since the mass of the load is `(4900" N")/(9.8" ms"^-2) = 500 " Kg"`, the initial momentum is `6.26times 500 " Kgms"^-1`

After the collision, this momentum is shared by the combined mass of `2000` Kg, which thus moves with a common speed of `~~1.6" ms"^-1`.