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some basic physics questions

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?

Reply 1

Nylex

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.

Reply 2

intr3pid

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.

Reply 3

moleo

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
=0.204g
Resolve left right
X(unknown force) - 0.204g (frictional force) = 1/2 a
a = 0
X - 0.204g = 0
X=0.204g
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".