1. If the horizontal force of the road on the tires of a 1200-kg car is a consta

Question

1. If the horizontal force of the road on the tires of a 1200-kg car is a constant 2000 N, how long will it take for the car to reach30 m/s starting from rest?

2. A man with a mass of 80 kg running at a speed of 5 m/s jumps onto a stationary skateboard with a mass of 4 kg. What is their combination speed?

3. A ball travelling to the right at 2 m/s strikes an identical ball, which is initially at rest. After the collision, the second ball is moving to the right at 3 m/s. What is the final velocity (magnitude and direction) of the first ball?

4. In reporting the results of an experiment your classmate claims that a red ball traveling to the right at 4 m/s struck a blue ball of the same mass, which was initially stationary. After the collision, the red ball was observed moving to the right at 3 m/s. Why is this observation impossible?

5. A 2-kg ball travelling to the right with a speed of 4 m/s collides with a 4-kg ball travelling to the left with a speed of 2 m/s. After the collision the 2-kg ball travels to the left at 2 m/s. What is the velocity of the 4-kg ball after the collision?

6. a 2-kg ball travelling to the right with a speed of 6 m/w collides with a 4-kg ball travelling to the left with a speed of 4 m/s. If the 2-kg ball recoils to the left at 1 m/s, what is the velocity of the 4-kg ball after the collision?

Please show work and explain.

Explanation / Answer

1) a = f/m = 2000/1200 = 5/3 m/s2

v = u + at => t = 18 s (u = 0)

Time is 18s

2) m1v1+m2v2 = MV (conservation of momentum)

80* 5 + 0 = 84 V => V = 4.762 m/s

Speed is 1.012 m/s

3) By conservation of momentum,

mv1+mv2 = mv3 + mv4 => 2 + 0 = 3 + v => v = -1 (mag = 1m/s towards left)

Velocity is 1 m/s towards left

4) This collision will be only in one direction (left-right)

By conservation of momentum as in above case, velocity of blue ball = 1 m/s toward right. and velocity of red ball = 3 m/s towards right. This is not possible since the red ball has to ccross the blue ball for this to happen physically.

5) By conservation of momentum

m1v1+m2v2 = m3v3 + m4v4

2*4 +4*(-2) = 2*-2 + 4 * v = > v = +1m/s (towards right)

Velocity is 1 m/s towards right

6) By conservation of momentum)

m1v1+m2v2 = m3v3 + m4v4

2*6 +4*(-4) = 2*-1 + 4 * v = > v = -0.5 m/s (towards left)

Velocity is 0.5 m/s towards left

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