Question

How much momentum will a dumbbell of mass 10 kg transfer to the floor if it falls from a height of 80 cm (assume that the dumbbell stops after hitting the ground)? (Take $g=10m{s}^{-2}$ )

• A. 40 kg m/s
• B. 50 kg m/s
• C. 30 kg m/s
• D. 35 kg m/s

Answer 1

The correct option is A

40 kg m/s

Given, mass of the dumb bell, m = 10 kg

Distance covered by the dumbbell, s = 80 cm = 0.8 m

Acceleration in the downward direction, $a$ = $10m{s}^{-2}$

Initial velocity of the dumbbell, u = 0

Let final velocity of the dumbbell(when it was about to hit the floor) = v
According to the third equation of motion
$v^2=u^2+2as$
$\Rightarrow v=\sqrt{u^2+2as}$
$\Rightarrow v=\sqrt{0+(2\times 10\times 0.8)}=4m{s}^{-1}$
Hence, the momentum with which the dumbbell hits the floor is
$m\times v=10\times 4=40kgm{s}^{-1}$