3/4 Markers

Question 1

Explain what will happen to the force on the wheel A as the load slides forward. (3)

Answer 1

Moment = force x perp. distance from pivot

As load slides forward, distance from load to A is less

So force is greater to give the same moment

Question 2

Explain why a current is generated in a cool when a magnet is pushed into it. What happens when the magnet stops and why. (4)

Answer 2

Current is generated due to e.m. induction

Changing mag field in a coil generates current

Due to induced voltage generated

If mag stops, no change in mag field so no induced voltage

Question 3

Explain how an earth wire and fuse work together to keep electrical appliance safe. (4)

Answer 3

Earth wire connected to metal casing

If live wire touches metal casing, current takes easiest route through earth wire to ground

This high current blows the fuse

When current increases - fuse melts, breaks circuit, prevents fire and electrocution

Question 4

Explain why a racing car can only reach a max. top speed.

Answer 4

Foot flat on accelerator- max. constant thrust
Car accelerates because of forward thrust is greater than drag

As speed increases, drag increases

Until thrust = drag

No balanced force so no acceleration - top speed (terminal velocity)