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M1 Homework – Hints

January 29, 2013

Question 1: (June 2008 Q4)

Hint:

(i)

• Draw a diagram with the forces in the horizontal and vertical direction (remember the normal reaction and frictional force)
• If unsure what direction to mark the frictional force, it doesn’t matter, because if you find your final solution is negative, it was in the opposite direction
• Resolve horizontally

(ii)

• Use Fmax = uR
• Resolve vertically to find R and use your Fmax from part (i)

Question 2: (Jan 2012 Q2)

Hint

(i)

• Consider what information you have been given …. time (t), final velocity (v) and displacement (s).
• Consider what you are trying to find…. acceleration (a)
• Is there a formula connecting t, v, s and a?
• When writing deceleration, give it as a magnitude… i.e. ignore the negative sign from acceleration.

(ii)

• Use F=ma
• If you know the weight, how could you find the mass?
• Once you find the frictional force, use Fmax = uR to find u (u is meant to be mu)

Question 3: (Jan 2012 Q6)

(i)

• You are given u and v.
• Find a by using F=ma (resolve forces)
• Then find s by using the formula that connects v, u, a and s

(ii)

• Consider the return journey. u = 0 and s will be the answer from (i)
• Find a again by using F=ma
• Then find t by using the equation of motion that connects s, u, a and t
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