Topic 2 Mechanics Flashcards
How would the speed differ between two objects dropped from height, h, of different masses? (excluding resistive forces) [2]
[1] The speed would be the same
[1] mgh=1/2mv^2 exclude m because its on both sides
Explain how a ball dropped inside water will cause the water to gain GPE? [1]
[1] Although the water level has not changed water inside will be displaced up by the falling ball
A ball dropped in water will loose more gravitational potential energy than the water it displaces, explain. [2]
[1] water has less mass
[1] water has lower desnity/ moeved up same distance/ where the block was
Or
[1]Some energy has dissipated/lost to surroundings/converted to other forms K.E/internal energy/heat/sound
Or
[2]Mechanism: via friction or drag/because the block or water accelerates/as block hits the bottom
l
A block is moved horizontally against friction, explain the amount of work done by the wight and normal contact force. [2]
[1] no work done/zero
[1] because they are forces perpendicular to the motion
Finding the force on a work done-distance graph [2]
[1] Draw LARGE triangle
[1] gradient of line
State the Principle of Conservation of energy [2]
[1]Energy can be neither created nor destroyed
OR
Energy cannot be created/destroyed / total energy is not lost/gained
[1]merely transformed from one form to another / in a closed/isolated system
Explain why breaking distance more than doubles [4]
[1]Because speed is doubled and deceleration is unchanged, time [1] to be brought to rest is doubled/increased
[1] Since distance = speed x time [mark consequent on first] or s = ut + 1⁄2 at2
[1] the distance is increased by a factor of (about) 4
Or
Recognition that (speed)2 is the key factor (1)
Reference to v2 = u2 + 2as or rearrangement thereof or kinetic energy (1) [second mark consequent on first]
(Hence) distance is increased by a factor of (almost) 4 (1)
Describe a proportional line on a velocity time graph [1]
[1] UNIFORM acceleration (not constant)
Explain the term drift velocity [1]
[1] average mean/net/overall velocity of electron along wire [Not speed]
Explain why wire gets warm [1]
[1] Collision makes ion/atom vibrate more vigorously OR in collision energy is transferred to lattice
As a ball drops and bounces on a hard surface explain why the downward lines are straight and parallel with one another. [2]
[1] Lines represent acceleration on the ball, gradient
[1]acceleration is uniform (gravitational force with mass constant)
How does a straight on a velocity-time graph draw onto a displacement-time graph? [1]
[1] acceleration becomes a curve
What does the area under a velocity-time graph represent? [1]
[1] displacement
How do find the average speed of an object from a velocity-time graph? [2]
[1] find the total distance (area)
[1] divide by time (s=d/t)
Newton third law pairs [4]
-equal and opposite reaction
4 criteria [1] same magnitude [1] opposite directions [1] same type of force [1] act on different objects
