# A-level Physics (Advancing Physics)/Forces and Impulse in Collisions/Worked Solutions

**1. Escape velocity from the Earth is 11.2 km ^{−1}. How much impulse must be exerted on a 47000 kg payload to get it to travel away from the Earth?**

**2. Two billiard balls, of mass 10g, collide. One is moving at 5ms ^{−1}, and the other at 2ms^{−1}. After the collision, the first billiard ball is moving backwards at 4ms^{−1}. The collision takes 1 ms. What force was exerted on this ball?**

**3. What impulse and force were exerted on the second ball?**

The impulse was -0.09Ns and the force was -90N.

**4. A 60 kg spacewalker uses a jet of gas to exert an impulse of 10Ns. How many times would he have to do this to reach a speed of 1 ms ^{−1} from stationary?**

So, the spacewalker would have to do this 6 times to reach a speed of 1ms^{−1}.

**5. A 5 kg bowling ball collides with a stationary tennis ball of mass 0.1 kg at 3ms ^{−1}, slowing to 2.5ms^{−1}. It exerts a force of 100N on the ball. How long did the collision take?**