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AS Mechanics Questions - Forces and Newton's Laws

1) An object is hung from a spring balance suspended from the roof of a lift. When the lift is descending with uniform acceleration 0.8ms^-2 the balance indicates a weight of 245N. When the lift is ascending with uniform acceleration ams^-2 the reading is 294N. Find the value of a.

2) An engine and train weigh 250 tonnes. The engine exerts a pull of 1.5 x 10^5N. The resistance to motion is 1/100 of the weight of the train and its braking force is 1/10 of the weight. The train starts from rest and accelerates uniformly until it reaches a speed of 45kmh^-1. At this point the brakes are applied until the train stops. Find the time taken for the train to stop to the nearest second.

Anyone have any idea on how to solve these?
Original post by TeeB123
1) An object is hung from a spring balance suspended from the roof of a lift. When the lift is descending with uniform acceleration 0.8ms^-2 the balance indicates a weight of 245N. When the lift is ascending with uniform acceleration ams^-2 the reading is 294N. Find the value of a.

2) An engine and train weigh 250 tonnes. The engine exerts a pull of 1.5 x 10^5N. The resistance to motion is 1/100 of the weight of the train and its braking force is 1/10 of the weight. The train starts from rest and accelerates uniformly until it reaches a speed of 45kmh^-1. At this point the brakes are applied until the train stops. Find the time taken for the train to stop to the nearest second.

Anyone have any idea on how to solve these?


not sure but for the first one, work out the mass using f=ma

then use the m and f value given to work out a


for the second one, work out the force in the direction of the train and divide it by its mass to get the acceleration of the train

using f =ma and rearranging for a

then use the fact that its initial speed was 45 and final speed of 0, acceleration of the value u got

use suvat

s =
u = 45
v = 0
a = value u got
t = ?

rearrange for t using v = u + at
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TeeB123
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Thank you! :smile:

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