2. What is the magnitude of the (upward) impulse generated by the normal force o

Question

2. What is the magnitude of the (upward) impulse generated by the normal force of Christine during the time interval of her jump off the plate?

3. What is the magnitude of the downward impulse due to gravity during this interval?

4.  What is the net impulse which propels her upwards when she jumps off the plate? (Recall, the net force on her is the normal force minus the force of gravity.)

5. What is her change in speed upwards for this process?

The diagram shows the normal force on Christine's feet vs. time, as recorded by a force plate while she stands still initially (until point B), then jumps off the plate. When her feet leave the plate, the normal force is zero. position vs. time 1. What is Christine's mass? 2. What is the magnitude of the (upward) impulse generated by the normal force of Christine during the time interval of her jump off the plate? 3. What is the magnitude of the downward impulse due to gravity during this interval? 4. What is the net impulse which propels her upwards when she jumps off the plate? (Recall, the net force on her is the normal force minus the force of gravity.) 5. What is her change in speed upwards for this process?

Explanation / Answer

1.) mass = initial force / g

= 500/10 = 50 kg

2.) impulse = integral F.dt

= area under the curve during the jump

= 1/2 * (2.05 - 1.55) * (1500-500) + 1/2 * (2.1-2.05) * (500) + (2.05 - 1.55) * 500

= 512.5 N.s

3.) impulse due to gravity = mg.t = 50 * 10 * (2.1-1.55) = 275 N.s

4.) net impulse = 512.5 - 275 = 237.5 N.s

5.) impulse = change in momentum

237.5 = m*(change in speed)

237.5 = 50*(change in speed)

--> change in speed = 237.5/50 = 4.75 m/s

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