First slide

Centre of mass(com)

Question

The velocity of the CM of a system changes from ${\vec{v}}_{1} = 4 \hat{i} m / s to {\vec{v}}_{2} = 3 \hat{j} m / s$ during time $Δ t = 2 s .$ If the mass of the system is 10 kg, the constant force acting on the system is

Easy

A

25 N
B

20 N
C

50 N
D

5N

Solution

$\begin{array}{l} \vec{F} = m \frac{Δ {\vec{v}}_{cm}}{Δ t} = \frac{10 (3 \hat{j} - 4 \hat{i})}{2} = 5 (3 \hat{j} - 4 \hat{i}) \\ | \vec{F} | = 5 \sqrt{3^{2} + 4^{2}} = 25 N \end{array}$

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