# In Chapter 4, you found that when a karate strike hits wooden blocks, the hand undergoes an acceleration of -6.50e3 m/s2. Medical data indicates the mass of the forearm and hand to be about 0.700 kg. What is the force exerted on the hand by the block? Newton second law states that to accelerate an object having a mass `m` with acceleration `a` one needs to apply to it an external force `F` having the value

`F =m*a`

Thus in the case shown in problem the external force value is

`F =0.7*(-6.5*10^3) =-4550 N`

The minus sign...

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Newton second law states that to accelerate an object having a mass `m` with acceleration `a` one needs to apply to it an external force `F` having the value

`F =m*a`

Thus in the case shown in problem the external force value is

`F =0.7*(-6.5*10^3) =-4550 N`

The minus sign in front of the force shows that it is opposing the direction of motion of the hand.

Answer: the absolute value of the force exerted on the hand is 4550 N

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