A 60 kg cyclist travelling at 8 m/s applies the brakes and stops. What was the cyclist's initial momentum?

7.5 kg·m/s 68 kg·m/s 480 kg·m/s 120 kg·m/s

Why do airbags in cars save lives? Apply the concept of impulse.

Airbags reduce the momentum of the car by absorbing kinetic energy Airbags are made of a material that eliminates all impact forces Airbags increase the stopping time, reducing the peak force needed to produce the same change in momentum Airbags increase the mass of the driver to reduce acceleration

Two ice skaters are stationary and push each other apart. Skater A has a mass of 50 kg and moves away at 3 m/s. Skater B has a mass of 75 kg. What is Skater B's velocity? (Assume the system starts from rest.)

3 m/s in the same direction as Skater A 4.5 m/s in the opposite direction 2 m/s in the opposite direction to Skater A 1 m/s in the opposite direction

In an elastic collision, what is conserved in addition to momentum?

Thermal energy Kinetic energy Potential energy Total mass

A car crumple zone is designed to deform in a front-end collision. How does this protect the passengers?

It increases the mass of the car to reduce acceleration It stores kinetic energy as elastic potential energy It extends the collision time, reducing the average force transmitted to the passenger compartment It reduces the total momentum of the vehicle before impact

Where is the centre of mass of a uniform rectangular beam?

At the heaviest end of the beam At the geometric centre of the beam At the point where it is supported At the surface in contact with the ground

An SUV has a higher centre of mass than a sports car of the same mass and wheelbase. What stability implication does this have?

The SUV is more stable because it has more ground clearance The SUV is more likely to roll over in sharp turns because its centre of mass is higher Centre of mass height has no effect on rollover risk The sports car is less stable because it is lighter

A tower crane has a long jib (arm) on one side with a hook for heavy loads, and a shorter jib on the other side with a concrete counterweight. Why is the counterweight needed?

To add extra weight so the crane can lift heavier loads To reduce the tension in the lifting cable To shift the overall centre of mass back over the tower so the crane does not topple under load To prevent the jib from vibrating in the wind

A 1000 kg car travelling at 25 m/s collides with a stationary 1000 kg car and they stick together (perfectly inelastic collision). What is their combined velocity immediately after the collision?

25 m/s 0 m/s — the cars stop because the collision is inelastic 12.5 m/s 50 m/s

A tightrope walker carries a long balancing pole. How does this improve their stability?

The pole pushes against the rope to increase friction The pole increases the moment of inertia, slowing any sideways tipping and giving more time to correct balance The pole reduces the walker's weight so the rope sags less The pole stores potential energy that can be released to correct a lean

Which design change would most improve the rollover stability of a tall delivery van?

Increasing the vehicle's top speed rating Adding more payload to the roof Widening the wheelbase (distance between left and right wheels) Replacing the steel body with lighter aluminium panels