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    • Thread Starter

    1) A car travelling 70.0 km/h slows uniformly to 30.0 km/h over 70.0m.

    Calculate :
    a) find the acceleration (in m/s²)
    b) the time taken to slow to 30.0 km/h (in seconds)

    2) What is the speed of a rock (in m/s) after it has fallen 0.533km from rest?

    3) An 1800kg car is at rest until it is rammed by a 2500kg car travelling at 4.5 m/s. If the two cars remain locked together after they collide, what velocity will they share after the collision?

    Dunno why I'm posting here again, but meh.

    1. a. Convert your speeds to ms^-1 and then use v^2 = u^2 + 2as, solving for a.
    b. Convert again and use v = u + at.

    2. Use v^2 = u^2 + 2as, but convert that distance to metres.

    3. Conservation of momentum: total momentum before = total momentum after, ie. m1u1 + m2u2 = (m1 + m2)v here.
    • Thread Starter

    I have another question

    Determine the force required to pull a 0.500kg block at a constant speed of 2.5m/s, if the coeffcient of friction is 0.17.

    heh i had to think about this.If its moving at a constant speed a = 0.
    Reactional force = 1/2g
    Friction =uR= 1/2g x 0.17
    Resolve left right
    X(unknown force) - 0.204g (frictional force) = 1/2 a
    a = 0
    X - 0.204g = 0
    Basically X has to be equal to the frictional force for it to pull at a constant speed due to newton's first law.
    "All bodies will continue to move with uniform velocity unless they are acted on by a resultant force".
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