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2-1 (e) Vector form of the equation of motion

2-1 (e) Vector form of the equation of motion

Point 5 of 7 — Motion with Variable Acceleration and ForceQuestion bank: 0 questions (0 with pictures)

05 2-1 (e) Vector form of the equation of motion

Method

  • If F⃗ and S⃗ are given as vectors in i^,j^,k^, then v⃗=dS⃗dt, a⃗=dv⃗dt and F⃗=ma⃗ component by component.
  • To find v⃗ and S⃗ from F⃗(t), integrate each component separately, using the initial conditions.
  • If the resultant force is zero, the acceleration is zero and the velocity is constant (Newton's first law).
✍️ Worked examples

Example 13: A body of mass 2 kg moves under three forces F⃗1=ai^+j^, F⃗2=2i^−3j^, F⃗3=3i^+bj^ N, with displacement S⃗=(t2+1)i^+3t2j^ m. Find a and b.

Solution:

  • v⃗=2ti^+6tj^ and a⃗=2i^+6j^.
  • F⃗=ma⃗=4i^+12j^.
  • Sum of the forces: (a+5)i^+(b−2)j^.
  • a+5=4 gives a=−1; b−2=12 gives b=14.

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