First slide

Second law

Question

The velocity of a body as a function of time t is given as $\vec{v} = 2 t \hat{i} + t^{2} \hat{j} m / s$ . What is force acting on the body at t = 2 s if its mass is 4 kg?

Moderate

A

$(4 \hat{i} + 7 \hat{j}) N$
B

$(12 \hat{i} + 18 \hat{j}) N$
C

$(8 \hat{i} + 16 \hat{j}) N$
D

$(12 \hat{i} + 16 \hat{j}) N$

Solution

$\vec{a} = \frac{d \vec{v}}{dt} = 2 \hat{i} + 2 t \hat{j} at t = 2 s \vec{a} = 2 \hat{i} + 4 \hat{j} \vec{F} = m \vec{a} = 4 (2 \hat{i} + 4 \hat{j}) = (8 \hat{i} + 16 \hat{j}) N$

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