Mechanics AS question impossible!!!!!!! Watch

msar
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Hey,
Assessment question so no answers. Descriptive help is much appreciated as I lack brain cells.

A speeding van passes a police car. The van is travelling at 27ms^-1, and the police car is travelling at 15ms^-1. From the instant when the van is level with the police car, the police car accelerates uniformly at 3ms^-2 in order to catch the van. Work out
(a) the time taken until the police car is level with the van,
(b) the speed of the police car at this time.
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RDKGames
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(Original post by msar)
Hey,
Assessment question so no answers. Descriptive help is much appreciated as I lack brain cells.

A speeding van passes a police car. The van is travelling at 27ms^-1, and the police car is travelling at 15ms^-1. From the instant when the van is level with the police car, the police car accelerates uniformly at 3ms^-2 in order to catch the van. Work out
(a) the time taken until the police car is level with the van,
(b) the speed of the police car at this time.
This is basic SUVAT. You want to express the displacement of the police car (s_1) and the displacement of the van (s_2) in terms of t seconds after the van passes the police car.

You are looking for the solution to s_1 = s_2.

Makes sense why?

Then the speed part should be straightforward.
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begbie68
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(Original post by msar)
Hey,
Assessment question so no answers. Descriptive help is much appreciated as I lack brain cells.

A speeding van passes a police car. The van is travelling at 27ms^-1, and the police car is travelling at 15ms^-1. From the instant when the van is level with the police car, the police car accelerates uniformly at 3ms^-2 in order to catch the van. Work out
(a) the time taken until the police car is level with the van,
(b) the speed of the police car at this time.
Horizontal motion, so v-t graph is preferable to using SUVAT eqns directly.

compare areas and solve for time, then part (b) is simple.
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msar
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Thank you both of you mechanics geniuses!!!!!!!!!!!
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dont know it
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(Original post by msar)
Hey,
Assessment question so no answers. Descriptive help is much appreciated as I lack brain cells.

A speeding van passes a police car. The van is travelling at 27ms^-1, and the police car is travelling at 15ms^-1. From the instant when the van is level with the police car, the police car accelerates uniformly at 3ms^-2 in order to catch the van. Work out
(a) the time taken until the police car is level with the van,
(b) the speed of the police car at this time.
Hi, not sure if I am correct for part a), but is the answer 8 seconds.
For the van, u=27 and a=0?(since the speed is constant but i'm not sure).
For the police car, u=15 and a=3.

Then equating the displacements gives you t=8 and t=0.
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