Im struggeling on this question. please help if possible, would love an explanation!

 

1.    During a sprint start, a 69.8 kg athlete exerts constant horizontal and vertical forces of 955 N and 987 N respectively, against the starting blocks. This resulted in a change in horizontal velocity of 7.94m.s-1. Calculate the time over which the horizontal force was applied to the start blocks.

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Helpfull  replies would be appreciated... 

Im struggeling on this question. please help if possible, would love an explanation!

 

1.    During a sprint start, a 69.8 kg athlete exerts constant horizontal and vertical forces of 955 N and 987 N respectively, against the starting blocks. This resulted in a change in horizontal velocity of 7.94m.s-1. Calculate the time over which the horizontal force was applied to the start blocks.

 

Hmm, so if i'm right the athlete accelerates at the first starting position with given forces?

This is what i would say:

F(total) = F(horizontal) + F(vertical) = 987 + 955 = 1942N 
A = F/m = 1942 / 96,8 = 20m.s-2
So his acceleration is 20m.s-2

Now i stuck as theres no distance given (so it's not possible to calculate the time). Maybe it helped, maybe not 

Edited May 14, 201411 yr by Matrix

 

Hmm, so if i'm right the athlete accelerates at the first starting position with given forces?

This is what i would say:

F(total) = F(horizontal) + F(vertical) = 987 + 955 = 1942N 
A = F/m = 1942 / 96,8 = 20m.s-2
So his acceleration is 20m.s-2

Now i stuck as theres no distance given (so it's not possible to calculate the time). Maybe it helped, maybe not 

 

 

Nice Japanese skills, I have no idea what the heck you're talking about xD

By conservation of linear momentum;

 

Initial momentum = 0, final momentum = 69.8 x 7.94 kgms^-1.

 

Impulse due to horizontal force causes change in (horizontal) linear momentum - impulse = force x time, so we have 955 * t = dp.

 

Solve for t.

Cheers guys your responses are appreciated.