First slide

Work

Question

A body of mass 2kg at rest is acted on by two mutually perpendicular forces 6N and 8N simultaneously. Its kinetic energy after 10s is

Moderate

A

2500J
B

5000J
C

2.5 k J
D

Both 1 and 3

Solution

$\begin{array}{l} v_{x} = u_{x} + a_{x} t = 0 + \frac{6}{2} \times 10 = 30 {ms}^{- 1} \\ v_{y} = u_{y} + a_{y} t = 0 + \frac{8}{2} \times 10 = 40 {ms}^{- 1} \\ KE = \frac{1}{2} m (v_{x}^{2} + v_{y}^{2}) = \frac{1}{2} \times 2 \times (30^{2} + 40^{2}) \\ KE = \frac{1}{2} \times 2 \times 50 \times 50 = 2500 J \end{array}$

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